Mushroom Feta Turnovers

To make the dough, mix flour and salt together in a large mixing bowl.
Cut in half of the butter using two knives.
Alternatively, you can use your hands, until you have the butter and flour combined to make a coarse meal.
Add water and stir until dough forms a ball.
Place dough on a clean lightly-floured surface.
Lightly flour a rolling pin and roll out dough to about 1/4 inch thickness.
Cut half of the remaining butter into thin slices and lay out on 2/3 of of the dough, leaving about a 1-inch margin around the dough.
Fold the unbuttered third over, and then fold again.
Use the rolling pin and roll out the dough and repeat with the last remaining butter.
Fold dough into a smallish square, wrap in plastic wrap and stick in the fridge to chill for about an hour.
Meanwhile, to make the filling, dice up the mushrooms and saute with the butter.
Remove from heat and mix in feta crumbles.
Once dough is nice and chilled, remove from the fridge and cut in half.
Preheat the oven to 425 degrees.
Roll out the dough into a large rectangle.
Using a pizza roller, cut dough into roughly 4-inch squares.
Brush dough with beaten egg and place 2 tablespoons of the mushroom feta mixture into the squares.
Fold the squares into triangles and place on a lightly greased baking sheet.
Repeat with the other half of the dough.
Brush tops with beaten eggs and bake for 20 minutes.