How to cook potatoes with the sauce?

150 g fat, 20 g of onion, half a cup of tomato sauce, 1-2 teaspoons cumin, two cloves of garlic, and salt. Finely chopped onion fry, add salt cumin, crushed garlic, tomato sauce and water. Peeled, washed potatoes cut into cubes, fry in fat until browned, pour prepared sauce and simmer on low heat.