• 2 refrigerated pie crusts (or your favorite double-crust recipe)
• 2 cups frozen blueberries
• 1½ cups frozen raspberries
• 1½ cups frozen blackberries
• ¾ cup sugar
• ¼ cup cornstarch
• 1 tbsp lemon juice
• Pinch of salt
• 1 tbsp butter, cut into small pieces
• 1 egg, beaten, for brushing
• 1 tbsp coarse sugar, for sprinkling

1. Heat the oven to 425°F (220°C) and place a baking sheet on the lower rack to catch drips.
2. Press one crust into a 9-inch pie dish and chill while you make the filling.
3. In a large bowl, toss the frozen berries with sugar, cornstarch, lemon juice and salt until evenly coated. Do not thaw the berries first.
4. Pour the filling into the crust and dot with butter.
5. Cut the second crust into strips and weave a lattice over the top. Trim and crimp the edges.
6. Brush the lattice with beaten egg and sprinkle with coarse sugar.
7. Bake for 20 minutes, then lower the oven to 375°F (190°C) and bake 50-60 minutes more, until the crust is deep golden and the filling bubbles thickly through the lattice. Cover the edges with foil if they brown too fast.
8. Cool for at least 3 hours before slicing so the filling can set.

Baking with frozen fruit: keep the berries frozen until the moment they go into the bowl. Frozen fruit releases its juice more slowly in the oven, so the cornstarch has time to thicken it and the bottom crust stays crisp. Expect about 10 extra minutes of bake time compared with fresh berries.