Flaky Cinnamon Apple Slab Pie with a Brown Sugar Crumble

Slab pie is what happens when you need to feed a crowd but refuse to make twelve individual tarts. The filling-to-crust ratio is different from a standard round pie, more generous on the apple side, and the flat format means every single slice has a clean edge of crust rather than a soggy underside. I added a brown sugar crumble over the top because it bakes into something irresistible.

This apple slab pie has become my go-to for every autumn gathering that needs a showstopper without the stress.

Why You Will Love This Recipe

• The sheet pan format feeds up to 20 people from one single bake, making it perfect for potlucks, holiday tables, and family gatherings.
• A double layer of buttery flaky pastry on the base keeps every slice sturdy and clean to serve.
• The brown sugar crumble on top bakes into a crunchy, caramelized crust that makes this look and taste bakery-made.
• The cinnamon apple filling is thick and jammy with no excess liquid to make the base soggy.
• Leftovers keep beautifully for two days and reheat in minutes.

Ingredients

For the pastry:

• 3 cups (375g) all-purpose flour
• 1 teaspoon fine salt
• 1 tablespoon granulated sugar
• 1 cup (225g) unsalted butter, very cold and cubed small
• 8 to 10 tablespoons ice cold water

For the apple filling:

• 2.5 kg (about 8 large) apples, peeled, cored, and thinly sliced (Granny Smith or a mix of Granny Smith and Honeycrisp)
• 3/4 cup (150g) light brown sugar, packed
• 2 tablespoons cornstarch
• 2 teaspoons ground cinnamon
• 1/4 teaspoon ground nutmeg
• 1/4 teaspoon ground allspice
• 1 tablespoon fresh lemon juice
• 1 teaspoon pure vanilla extract

For the brown sugar crumble:

• 1 cup (125g) all-purpose flour
• 1/2 cup (110g) light brown sugar, packed
• 1/2 teaspoon ground cinnamon
• 1/4 teaspoon fine salt
• 1/2 cup (115g) unsalted butter, cold and cubed small

For finishing:

• 1 egg, beaten (for egg wash)
• 1 tablespoon coarse sugar for sprinkling

Crockery and Time To Create

Equipment: Large rimmed baking sheet (18×13 inch half sheet pan), rolling pin, large mixing bowl, pastry cutter or fork, sharp knife or mandoline for apple slicing, pastry brush
Total Time: 1 hour 35 minutes (30 minutes prep + 20 minutes chilling + 45 minutes bake)
Yield: 18 to 20 slices

Ingredient Substitutions and Variations

• Granny Smith Apple: A mix of Granny Smith and Honeycrisp gives a balance of tart and sweet that works beautifully in this filling.
• Cornstarch: Arrowroot starch is a direct substitute and gives a slightly clearer, glossier filling.
• Light Brown Sugar (filling): Dark brown sugar adds a deeper molasses note to the filling if you prefer a richer flavor.
• Unsalted Butter (pastry): Keep it very cold. Room temperature butter will not produce a flaky layered crust.
• Brown Sugar Crumble: Rolled oats at 1/4 cup mixed into the crumble add a hearty texture variation.

Step-by-Step Instructions

• Make the pastry first. In a large bowl, whisk together the flour, salt, and sugar. Add the cold cubed butter and press it into the flour using your fingertips or a pastry cutter until the mixture resembles rough, uneven crumbles with some pea-sized butter pieces still visible. These butter chunks are what create the flaky layers. Add ice water one tablespoon at a time, tossing with a fork after each addition, until the dough just comes together when pressed. It will look shaggy. Divide into two equal portions, flatten into discs, wrap, and refrigerate for at least 20 minutes.

• While the pastry chills, make the apple filling. Peel, core, and thinly slice the apples to about 3mm thickness. In a large bowl, toss the sliced apples with brown sugar, cornstarch, cinnamon, nutmeg, allspice, lemon juice, and vanilla until every slice is coated. Set aside.
• Make the brown sugar crumble. In a bowl, combine the flour, brown sugar, cinnamon, and salt. Add the cold cubed butter and press it into the dry ingredients with your fingertips until the mixture forms rough clumps ranging from pea-sized to almond-sized. Refrigerate until needed.
• Preheat your oven to 400°F (205°C). Remove one pastry disc from the fridge. On a lightly floured surface, roll it out to a rectangle slightly larger than your 18×13 inch baking sheet, about 20×15 inches. Carefully transfer it to the baking sheet, pressing it into the corners and allowing the excess to hang over the edges.
• Spread the apple filling evenly over the pastry base, distributing the apple slices in an even layer all the way to the edges. Scatter the brown sugar crumble evenly over the entire apple surface, covering it generously. Fold the overhanging pastry edges up and over the crumble border, pressing gently to seal and create a rustic frame around the filling. Brush the folded pastry border with beaten egg and sprinkle with coarse sugar.

• Bake for 40 to 45 minutes until the pastry border is deeply golden, the crumble is caramelized and set, and the apple filling is bubbling at the edges. If the crumble browns too quickly, tent loosely with foil for the last 10 minutes. Cool in the pan for at least 20 minutes before slicing.

Pro Tips for Best Results

• Keep every element of the pastry cold at every stage. Cold butter hitting a hot oven is what creates steam and produces flaky layers.
• Slice the apples thin and uniform so they cook through completely during the bake without leaving hard undercooked pieces in the filling.
• The cornstarch thickens the apple juices during baking and prevents the base from getting soggy. Do not skip it or reduce the amount.
• Cool the slab pie for at least 20 minutes before cutting or the filling will run. It slices cleanly once it has had time to set.

Common Mistakes to Avoid

• Using warm butter in the pastry: Even slightly soft butter produces a dense, cracker-like crust rather than a flaky layered one. Keep everything cold throughout.
• Skipping the cornstarch: Apples release a significant amount of liquid during baking. Without a thickener, the base will be wet and the filling will slide when you cut slices.
• Overfilling the edges: Leave a clear 2-inch border around the filling so the pastry edge can fold up cleanly and hold its shape during baking.

What to Serve With

• A generous scoop of vanilla bean ice cream melting over a warm slice is the classic pairing and it works perfectly every single time.
• Lightly whipped cream with a pinch of cinnamon stirred in complements the spiced apple filling without competing with it.
• A drizzle of warm salted caramel sauce over the top just before serving turns this into a full dessert centerpiece for a dinner party.

Storage and Reheating

• Room temperature: Cover loosely and store for up to 2 days. The crumble stays reasonably crisp.
• Refrigerator: Store covered for up to 4 days. The crust softens slightly but the flavor deepens.
• Freezer: Freeze individual slices wrapped in foil for up to 3 months. Thaw overnight in the fridge.
• Reheating: Warm in a 325°F oven for 12 to 15 minutes until heated through and the crumble crisps again. Avoid microwaving as it softens the pastry.

Nutrition Information

Health Benefits

Apples are one of the most fiber-rich fruits available in everyday baking, with both soluble and insoluble fiber that supports digestive health and helps maintain steady blood sugar levels after eating. Using a generous amount of fresh apple in this recipe means each slice contributes real nutritional value alongside the indulgence.

Cinnamon, allspice, and nutmeg are not just flavor additions here. All three contain antioxidant compounds that have been studied for their role in reducing inflammation and supporting metabolic health, making this spiced filling genuinely more beneficial than a plain sugar-only version.

Conclusion

Apple slab pie is one of those recipes that makes you look like you spent far more time than you did. The flaky crust, the jammy spiced filling, the caramelized crumble on top. Whether you are making this for Thanksgiving, a school bake sale, or a weekend gathering, it will be gone before you expect it. Save this recipe now and share it with anyone who loves apple pie but needs to feed more than six people.

Flaky Cinnamon Apple Slab Pie with a Brown Sugar Crumble

A crowd-serving sheet pan apple pie with a buttery flaky crust, thick cinnamon apple filling, and a caramelized brown sugar crumble on top.

Print Recipe Pin Recipe

Prep Time 30 minutes mins

Cook Time 45 minutes mins

Chill Time 20 minutes mins

Total Time 1 hour hr 35 minutes mins

Servings: 20 people/slices

Calories: 312

Ingredients Equipment Method

Ingredients

  

Pastry: 3 cups flour, 1 tsp salt, 1 tbsp sugar, 1 cup very cold cubed butter, 8-10 tbsp ice water

Filling: 2.5kg apples peeled and thinly sliced, 3/4 cup brown sugar, 2 tbsp cornstarch, 2 tsp cinnamon, 1/4 tsp nutmeg, 1/4 tsp allspice, 1 tbsp fresh lemon juice, 1 tsp vanilla

Crumble: 1 cup flour, 1/2 cup brown sugar, 1/2 tsp cinnamon, 1/4 tsp salt, 1/2 cup cold cubed butter

Finishing: 1 beaten egg, 1 tbsp coarse sugar

Equipment

• 1 Large rimmed baking sheet (18×13 inch half sheet pan)
• 1 Rolling Pin
• 1 large mixing bowl
• 1 Pastry cutter or fork
• 1 sharp knife or mandoline for apple slicing
• 1 pastry brush

Method

 

Make pastry, divide into two discs, refrigerate 20 minutes.

Toss sliced apples with all filling ingredients. Set aside.

Make brown sugar crumble, refrigerate until needed.

Preheat oven to 400°F. Roll one pastry disc to fit sheet pan, press in with overhang.

Spread apple filling evenly. Top with crumble. Fold pastry edges up to form border. Egg wash the border, sprinkle coarse sugar.

Bake 40 to 45 minutes until golden and bubbling. Cool 20 minutes before slicing.