Incredibly easy and delicious! Everyone who tries it will ask for more

Incredibly easy and delicious! Everyone who tries it will be asking for more.
Ingredients:
For the dough:
1 egg
2.5 cups water
6 cups flour
1 teaspoon salt
To grease the dough: 7 ounces (200 g) butter
For the filling:
14 ounces (400 g) ground beef
2 onions
1 teaspoon black pepper
1 teaspoon red pepper
Salt to taste
To brush the top:
1 egg yolk
1 teaspoon milk