Mixed Berry Slab Pie for a Crowd

Before you start

A slab pie is a regular double-crust fruit pie stretched across a rimmed sheet pan. It serves a crowd, travels well, and cuts into neat squares that are easy to eat by hand. The crust-to-filling ratio is higher than in a round pie, so every piece has plenty of flaky pastry, and the shallow filling bakes and sets faster.

The challenge is scale. You need a large batch of dough that stays cold while you roll it into a big rectangle, and a filling with enough thickener for a pan this size. Rolling the dough between sheets of parchment and chilling it before lining the pan makes the job manageable. Mixed berries give color and balance, but the same method works with any fruit pie filling.

Ingredients

• Crust560 g (4½ cups) all-purpose flour
• 2 tbsp granulated sugar
• 2 tsp fine salt
• 400 g (1¾ cups) unsalted butter — cold, cubed
• 180–240 ml (¾–1 cup) ice water
• Filling1.6 kg (about 11 cups) mixed berries — blueberries, blackberries, raspberries and quartered strawberries; fresh or frozen
• 250 g (1¼ cups) granulated sugar
• 64 g (½ cup) cornstarch
• 2 tbsp lemon juice
• 1 tbsp finely grated lemon zest
• ½ tsp fine salt
• Finish1 large egg — beaten with 1 tbsp water
• 2 tbsp turbinado sugar
• Glaze (optional)120 g (1 cup) powdered sugar
• 2–3 tbsp lemon juice

Method

1. Whisk the flour, sugar and salt in a large bowl. Cut in the cold butter until the pieces are pea-sized with some larger flakes. Add 180 ml ice water and toss, adding more a tablespoon at a time until the dough holds. Divide it into two portions, one about 60 percent of the dough, shape into flat rectangles, wrap and chill for 1 hour.
2. Roll the larger portion between two sheets of parchment into a 43 × 33 cm (17 × 13 in) rectangle about 3 mm thick. Roll the smaller portion into a 38 × 28 cm (15 × 11 in) rectangle. Slide both, still in parchment, onto trays and refrigerate for 30 minutes.
3. Peel off the top parchment from the larger sheet, flip it into the pan, and peel off the second sheet. Ease the dough into the corners and up the sides, letting it hang over the rim.
4. Heat the oven to 200°C (400°F) with a rack in the lower third and a second baking sheet or foil on the rack below. Whisk the sugar, cornstarch, zest and salt in a large bowl, add the berries and lemon juice, and toss until coated. Use frozen berries straight from the freezer.
5. Spread the filling evenly in the lined pan. Lay the top sheet over it, trim both layers to a 1.5 cm overhang, fold the edges under and crimp with a fork. Brush with egg wash, sprinkle with turbinado sugar, and cut a grid of short vents every 8 cm or so.
6. Bake for 45 to 55 minutes, until the crust is deep golden and the juices bubble thickly through the vents across the whole pan, including the middle. Frozen berries may need 10 minutes more.
7. Cool on a wire rack for at least 2 hours. If glazing, whisk the powdered sugar with enough lemon juice to make a thick but pourable glaze and drizzle over the cooled pie. Cut into 5 rows by 4 for 20 squares.

Tips for success

• Rotate the pan halfway through the bake; sheet pans often brown unevenly at the front and back of the oven.
• Patch tears with dough scraps and a dab of water rather than rerolling; reworked dough shrinks.
• Keep a ruler nearby. Rolling to measured sizes is the easiest way to get the dough to fit a rectangular pan.

Substitutions

Mixed berries

Use 1.8 kg sliced apples or stone fruit; reduce cornstarch to 45 g for apples and keep 64 g for juicy peaches or plums.

Top crust

Cover with a streusel of 200 g flour, 150 g brown sugar and 140 g melted butter for an easier, quicker topping.

All-butter crust

Replace 100 g of the butter with cold shortening for a more tender crust that is easier to roll in a warm kitchen.

Variations

Cherry-berry slab

Replace half the berries with pitted sour cherries and add ¼ tsp almond extract.

Lattice slab

Cut the top sheet into 2.5 cm strips and weave a lattice instead of venting a full crust.

Troubleshooting

Center of the pie is runny

The middle did not reach a boil. Bake until bubbles appear through the central vents, not only along the edges.

Dough tore while lining the pan

It was too warm or rolled too thin. Chill rolled sheets in parchment before moving them and keep them about 3 mm thick.

Bottom crust is pale

The pan sat too high. Bake in the lower third, and choose a light-colored aluminum pan over a thin dark one.

Storage

Store loosely covered at room temperature for up to 2 days, or refrigerate for up to 4 days. Squares freeze well, wrapped individually, for up to 3 months. Add the glaze after thawing for the best look.

Safety notes

Do not taste the raw dough, which contains uncooked flour. Contains wheat, milk and egg.