Preheat the oven to 350 degrees F (177 degrees C).
In a large bowl, mix the salt, flour, and water until a stiff dough is formed. Add more water if needed. Divide the dough into 2 equal parts.
On a floured surface, roll the dough out so it is large enough to fold over the whole duck.
Stuff the ducks with the rosemary and garlic. Place the duck on top of a rolled crust, breast-side down. Fold the crust over and lay seam-side down in a greased casserole pan. Repeat with the remaining duck.
Brush the egg over the top and sides of the wrapped ducks.