Pour warm, not hot milk into a bowl, add the yeast and sugar, stir until the yeast and sugar dissolve. Add the egg, salt, sour cream, butter, mix.
Gradually add sifted flour and knead a soft dough, not sticky to hands. It is not necessary to knead the dough for a long time. Grease a bowl with vegetable oil, put the dough into a ball, cover it with clingfilm and leave to rise for about 1-1.5 hours.
For stuffing cut chicken, potatoes and onions into small cubes. Add salt, pepper and mix everything thoroughly.
The dough has risen, becomes airy and porous.
Divide the dough into 12 equal parts and form balls. Roll out each ball into a layer with a diameter of about 14-15 cm. In the center put the filling (about 1.5 tbsp.).
Connect the edges of the dough, pinch well to form triangles, leaving a hole in the middle.
Place the triangles on a baking sheet lined with parchment paper. Brush with egg if desired. Bake in an oven preheated to 180 degrees. Bake the triangles for about 25-30 minutes until lightly browned.
Then take the tray out of the oven for juiciness of the filling pour a spoonful of broth (or water) into each triangle.
You can cover the triangles with foil to make the filling soft and juicy.
Bake for another 30 minutes or so, until the filling is cooked through.
Take out the ready echpochmaki, cover with a napkin and let cool.