Melt lard in a heavy casserole and add onion. Cook onion over low heat for 15 minutes.
Put in the beef and brown all sides over high heat for a few minutes. Push onion away from meat to the sides of the pan so meat can directly touch bottom of the casserole.
Add cut-up tomato, garlic and enough water to cover meat. Cook, covered, over very low heat, until meat is done.
Take out meat. Add to the cooking liquid the paprika, salt and green pepper. Reduce over high heat, without a cover, for 10 minutes. Make sure that the sauce does not burn, Then pass it through a sieve or purée in a blender.
Slice the meat and arrange it on a heatproof serving platter. Pour sauce over it. Return it to the heat for another 5 to 10 minutes, then serve.