You have to begin preparing this dish the night before. This does not mean you are supposed to cook all night - this is not at all customary for the Bulgarian cooking technique. You have to clean and wash the lentils and soak it in water, leaving it there for the night. On the next day begin with draining the lentils, then pour fresh water on it and boil on a moderate fire to softening. In a saucepan stew the finely chopped onion with the vegetable oil and a coffee cupful of water. When the onion grows yellowish, add the carrots and celery, cut up in small cubes. Add this mixture to the lentils, when almost ready, together with the garlic cloves (unpeeled), the tomatoes - peeled and grated, and the cubed potatoes. Boil on, till lentils become absolutely soft - then transfer to an oiled baking dish, salt to your liking and put dish in the oven. Bake in a moderately quick oven to get the potatoes soft too.
Note: This dish is very healthful for young children, old people and residents of countries with a cold climate, because it is very nutritious. Its wholesomeness is due to the heat processing applied - boiling and baking. When products are boiled, the nutritive substances are preserved, and when baked - products are processed in a way that makes them most easy to assimilate.