COOKING PIES WITH POTATO !!!

Dough:
Kefir - 350 ml
salt - 1 teaspoon
sugar - 1 teaspoon
egg - 1 piece
vegetable oil - 50 ml
flour - 500 gr (+-)
baking powder - 1 teaspoon
for filling;
Potatoes - 800 gr boil
fried onion - 1 piece
salt + pepper to taste
Frying oil