Dissolve yeast in 0.5 cup of warm water, add sugar, stir and leave for 20 minutes, until the mixture is frothed. Melt the butter and add it to the yeast with the milk. Pour half of the flour into the resulting mixture, knead the dough and place in a warm place for 40 minutes. Then add the remaining flour, stir well and leave for another hour. Prepare the filling. Wash meat and dry it. Peel potatoes and onion. Cut meat, potatoes and onion into identical cubes in size slightly less than a hazelnut. Put in a bowl, add softened melted butter, salt and pepper and stir thoroughly. Cover and leave for 1 hour. Floor the cooking table, divide the dough into 6 parts and roll out each part into a flat cake. Put 1,5-2 tbsp. filling on the flat cakes. Pinch the edges in the form of a triangle, leaving a hole in the middle. Roll balls of suitable diameter from the remains of the dough and cover the holes in patties. Preheat the oven to 190 ° C. Lay the echpochmaks out on a greased baking sheet and leave for 10 minutes. Then coat with a slightly beaten-up egg and bake for 20 minutes. Take the patties out of the oven, open the holes and pour 2 tbsp. of broth in each one. Cover the patties again with balls and put back to the oven for another 20 minutes.