Prepare the dough. Pour kefir into a deep bowl, warm it up slightly, dissolve the yeast, add sugar, salt and egg. Mix, add flour and knead a dense dough. Let the dough rise for 10-15 minutes. Divide into 2 parts, roll each into a thin rectangle. Grease the first rectangle with butter. Put the second rectangle on it, grease the top with butter. Roll both layers together into a tight tube, cut into two parts, wrap in cling film and refrigerate for 2 hours.
Prepare the filling. Combine the onion with the minced meat, add salt, pepper and cumin. Mix thoroughly.
Prepare the samsa. Take the dough, cut into squares, roll it out a little and put the filling in the center of each piece. Shape the pastry into a triangle. Let it sit on the table for 15 minutes. Preheat the oven to 180 degrees. Cover the baking sheet with parchment. Grease the samsa with yolk, put it on the baking sheet. Sprinkle with sesame seeds. Bake for 40 minutes.