2 cups flour
1/2 cup granulated sugar
1 stick of unsalted cold butter
1 medium egg at room temperature
1 egg yolk at room temperature
1/6 teaspoon salt
1/2 teaspoon baking powder
zest of half a lemon
1 cup bilberry preserves

1. Put the flour in a pile on a board and make a pit in it. Add sugar, baking powder, salt, lemon zest, and the eggs in the pit.
2. Add the cold butter cut into small pieces in the pit. Mix it in quickly to avoid overheating the butter and causing the taste to be altered.
3. Form the dough into a ball and wrap it in cling film. Leave it for at least an hour in a fridge.
4. Remove a third of the loaf and leave the third in the fridge. The other two-thirds you are going to use right now. Roll them out until they reach a thickness of a quarter inch. Place the pastry dough in a tart mold. The mold is best with a removable bottom to take the tart out of the mold when the baking is finished.
5. Take a piece of the third in the fridge and make a long roll of dough the thickness of a finger. Then place the roll around the pastry dough already in the mold. Use fork tines to press on the dough until it becomes relatively flat. Then, pour the bilberry preserves in the center of the crostata and use a spoon to spread it over the whole surface of the tart.
6. Finally, take the rest of the third in the fridge and make more rolls of pastry. Flatten them and lay them out on the surface of the preserves to make a criss-cross pattern.
7. Bake in an oven at 350F for about 30 minutes, or until it is golden brown. Let it cool for at least 2 hours before serving.