Blueberry Strawberry Lattice Tarts with Cornmeal Crust

Steps

1. Make the crust: in a large bowl whisk the flour, cornmeal, 70 g of the sugar (about a third), the salt and the baking powder.
2. Add the softened butter and the beaten egg and mix with a spatula, then your hands, until a soft, even dough forms.
3. Divide the dough: weigh out about one third for the lattice, shape it into a flat rectangle, wrap and chill it for 30 minutes.
4. Split the remaining two thirds in half and press each half evenly over the bottom and up the sides of a 9-inch (23 cm) tart pan with a removable bottom. Chill the tart shells while the lattice dough chills.
5. Preheat the oven to 400°F (200°C) with a rack in the lower third and a rimmed baking sheet on it.
6. Make the filling: in a bowl stir together 120 g of the sugar, the cornstarch and the lemon zest, then gently fold in the blueberries, strawberries and orange juice. Divide the filling evenly between the two chilled tart shells.
7. Roll the chilled lattice dough between two sheets of parchment to about 1/8 inch (3 mm) thick and cut into 1/2-inch (1.3 cm) strips. If the strips get soft, chill them for 5 minutes.
8. Weave half the strips over each tart in a lattice and press the ends into the crust edges; patch any breaks by pressing them together.
9. Brush the lattice with the milk and sprinkle with the remaining 10 g of sugar.
10. Set both tarts on the hot baking sheet and bake for 15 minutes, then lower the oven to 375°F (190°C) and bake 30 to 35 minutes more, until the lattice is deep golden and the filling bubbles thickly in the center.
11. Cool the tarts in their pans on a rack for at least 2 hours so the filling sets, then remove the rings and cut each tart into 6 slices.