Preparation of the dough:

1. Mix the dry ingredients in a bowl: flour, powdered sugar, and salt. Add the butter and mix a little making it look crumby. Add the lemon juice, egg, and water. Mix until everything is united, it is not necessary to knead too much.
2. Wrap the dough in a plastic and bring to the refrigerator for 30 minutes.
3. Meanwhile prepare the filling, by cutting the peaches and plums into slices and removing their seeds. In a small bowl mix the flour, cornstarch, and sugar, add the butter and vanilla extract. Unite with the fingers to make a crumby mixture and add the peaches and plums. Let it rest for a while.
4. Remove the dough from the refrigerator after 30 minutes, and divide the dough into 3 equal parts.
5. Join two of those parts, and extend the dough with the help of a rolling pin, then place it in a non-stick or buttered mold. Leave some edges on the sides, and try to even everything out.
6. Add the filling.
7. Then, with the third part of the dough, stretch it with a rolling pin, ideally with plastic wrap on top of the dough so that it doesn’t stick to the rolling pin. Then cut the dough in strips. Place the strips interspersed over the pie very carefully.
8. In a small bowl, beat 1 egg with 1 tablespoon of water, and a pinch of salt. Brush the pie with this mixture and then sprinkle with sugar.
9. Take to the oven at 400°F (200°C) for 10 minutes. Then lower the temperature to 350°F (180°C) and bake for 45 minutes.
10. Serve when completely cold.