Heat the milk and water and then add them to the mixer. The ideal temperature of the liquid elements should be between 30 and 40 degrees Celsius so that they do not destroy the yeast.
Add the sugar and dry yeast into the mixer bowl, stir gently and wait about 10 minutes for the yeast to turn on. Then add the melted butter, flour and finally the salt into the mixer.
Knead with the dough hook for 5 to 10 minutes. The dough should be moist enough to stick. Pour some flour on a clear surface and knead the dough by adding some flour over it. The dough should not stick too much in the end.
Place the dough in an oiled bowl and cover with a clean towel. Wait for about 1 to 1.5 hours for our dough to double.
Meanwhile, prepare the filling. Chop the mushrooms and saute for 10 minutes over medium heat. Withdraw from the fire.
In a large bowl add the grated cheeses, while in the other one the mushrooms, salt and freshly ground pepper. Set aside.
Once the dough has doubled, preheat the oven to 250 * C.
Dust a clean surface with some flour and divide the dough into two equal parts. With a rolling pin, roll out the dough into a rectangular shape and then cut in half. Along both sides, add grated cheese (about half for all 4 pizza boats), leaving a gap in the middle.
Grab each side and slice it over the cheese mixture to form the sides of the pizza boat. This way the dough will cover the cheeses. Stick together the two edges of the pizza boat. Add the remaining half of the cheese mixture into the center of the pizza boat and then the mushrooms.
In a pan, add parchment cooking paper and then transfer the pizza boats. Bake at 250 * C for about 18 to 20 minutes. Once removed from the oven, add some butter to the filling of each pizza boat and let it melt.