1. Peel the small onions. Heat up 3 spoonfuls of oil on a frying pen and fry the entire onions, over a high flame, until they get brown.
2. Add salt and pepper, add the stock and let it cook over a low flame, with the lid on, during 20 minutes. Stir from time to time.
3. Cut the liver, the spleen, the lung and the heart (or the selected entrails) into pieces. Clean them very well with cold water. Dry with kitchen roll.
4. Heat up the oil in a pan and turn golden all the entrails, jointly with the chopped garlic, during some minutes. Add salt and pepper, baste in Jerez and let it evaporate over a low flame.
5. Add the peeled and cut into pieces tomato, with no seeds. Stir, put the lid on and cook during 15 minutes. Stir from time to time.
6. Add the onions at the end of the cooking and cook during 2 more minutes. Add more salt and pepper if necessary. Serve.