Prepare the picadillo: Cut the meat into large cubes. Put them into the pan with the onion, garlic, and salt and cover with cold water. Bring the meat to a boil, lower the flame and let it simmer until just tender--about 40 to 45 minutes. Do not overcook. Leave the meat to cool off in the broth. Strain the meat, reserving the broth, then shred or chop it finely and set it aside. Let the broth get completely cold and skim off the fat. Reserve the fat. Melt the lard and cook the onion and garlic, without browning, until they are soft. Add the meat and let it ook until it begins to brown. Crush the spices roughly and add them, with the rest of the ingredients to the meat mixture. Cook the mixture a few moments longer. Mash the tomatoes a little and add them to the mixture in the pan. Continue cooking the mixture over a high flame for about 10 minutes, stirring it from time to time so that it does not stick. It should be almost dry. Prepare the walnut sauce: Cover the nuts with boiling water and leave them to soak for 5 minutes. (If you leave them soaking too long the skin will become too soft and will be more difficult to remove.) Remove the papery brown skin--it should come off quite easily.