Prepare the sourdough: add crumbled yeast in the warm milk, also add sugar and some flour, mix gently and leave in the dar place for 30 minutes. Mix with the flour and knead the elastic dough, add the melted butter and salt in the end, knead thoroughly and longly. Leave to rise, then roll out and cover the form with the dough(the bottom and sides). For the filling: simmer the diced onion in the butter until golden brown, add the flour, mix well and cool. Place the filling into the form. Beat eggs with cream, season with salt and pour over the filling, sprinkle with diced bacon and cumin, butter flakes. Bake in the oven at 200 degrees Celsius for 35-45 minutes, serve warm.