Wash spinach in cold running water.
Drain and squeeze out excess water and roughly chop. Blend in a blender together with half ricotta.
In a large bowl, combine to the rest of ricotta and mix thoroughly. Add salt, Parmesan cheese and cheddar.
On a lightly floured surface, roll the dough into a thin rectangle and cut out circles out of the pastry by pressing into it the border of a glass (use a 4-inch round cookie cutter, if you have it).
Press each circle into the bottom of a greased cupcake tin for the bottom of the pie crust. Repeat with remaining dough until 16-18 muffin tins are filled.
If some pastry will hang over the sides of the tin, just trim the borders with a knife.
Spoon the filling into the tins and cover with a traditional crust tops you obtain by cutting out small circles from the remaining pastry.
Brush each pie crust with the egg wash (egg yolk mixed with milk). Chill in fridge for at least half an hour.
Bake for 25-30 minutes.