While the vegetables are cooking, prepare the roast:
fry the onion in lard, add chopped tomatoes, bell pepper and fry.
Then add tomato paste and sour cream to the fried, yes, sour cream. Simmer over low heat, stirring constantly. You will learn about the readiness of frying by the red color of the oil that appeared on the surface.
PS.: at first I was worried, thinking that I put too much sour cream. But everything is fine, in 15-17 minutes the color changed from white to bright red, the sour cream evaporated completely.