In a heavy bottom pan (I prefer ceramic coated), begin to sauté the minced vegetables with oil and lard (or butter). Add some salt and paprika. On a slow flame cook and stir until the onion becomes translucent. Move the vegetables to one side. Pat the roast dry and add it to the pot. Brown each side, then add the tomatoes. Lower the heat to the lowest setting possible, to keep at a very low simmer; if necessary, use a heat diffuser. Add the whole glove of garlic and bay leaf, and sprinkle in a little more salt. Cook for about 8 hours, turning the roast every 2 hours. (You may use an electric slow cooker if you like.) I know that the dish is ready from the color and consistency of the sauce: dark red-brown with a golden circle of oil emerging at the top. But a simpler way to know is by dipping bread in it after about 6 hours and tasting it, adding further salt if needed.