In a bowl, mix mushrooms and water. Cover with microwave safe plastic wrap and microwave 30 seconds. Cool down 5 minutes. Drain while keeping soaking water. Chop mushrooms and set aside.
In a casserole, heat oil at medium heat and steam leeks and garlic for about 4 minutes. Add millet, dry mustard, ras el hanout and mushrooms, mix and continue cooking 1 minute.
Pour soy sauce, broth and mushrooms soaking water. Bring to a boil, cover and simmer at medium-low heat for 20 minutes, until almost all liquid is absorbed.
Prepare dough. Preheat oven at 375 °F (190 °C).
In a blender, mix flour and salt. Add butter and, with the help of the intermittent function of the blender, activate 4 times for 1 seconds. Add egg and water, and continue to mix, still intermittent, 1 second at a time, until small chunks of dough starts to take form.
Remove dough from blender and form a ball. Divide dough into two portions, one lightly bigger than the other one.
Over a floured work surface, lay down the biggest ball of dough into a dough portions of 0.25 (1/8 inch) thick. Press down a pie mold of 23 cm (9 inches). Lower remaining dough the same way.
Add mozzarella to the millet preparation, mix, then pour the preparation into the pie dough. Cover with another dough and seal dough sides of the pie.
Brush with roasting mixture, then cook at the bottom of the oven for about 45 minutes, until the pie is well colored. Cool down 10 minutes before serving.
Chef’s note
Ras el hanout may be replaced by a mix of cinnamon, coriander and ground cardamom.