Preheat the oven to 425 degrees.
While the dough is chilling, combine gently the fruit and the sugar, nutmeg, lemon, flour and salt.
Once the dough is rolled out, place the filling in the middle, leaving about 2-3 inches clear of the filling as you will be folding it on top of the filling to form the edges.
Add the crumble as instructed below. Then fold the edges: take 2-3 inches and fold on top of the filling, then fold the next 2-3 inches, slightly layering on top of the last folded edge. Do this until the edges are all folded on top of the filling. Make sure not to break the dough as this will allow leaking of the filling while cooking (however, if this happens, it is absolutely okay and still very delicious).
Brush the dough with the egg white and water mixture.
Place in the oven for 20 minutes. Reduce heat to 375 degrees. Bake for 30-35 minutes more until crust is brown and filling is slightly bubbling. Remove from the oven and let cook for 5-10 minutes.
Serve warm with gelato or ice cream.