Every Roman family eats the traditional baby lamb on Easter Sunday. It is a custom as firmly entrenched as turkey at American Thanksgiving. The best lambs come from around Rome, and are milk fed, which gives them a pale, tender meat. Once the lambs begin grazing, the flesh becomes darker and stronger. The following recipe comes from Anna Maria's ninety-four- year-old aunt, who is a Roman. She came into the kitchen with us to teach us because she is accustomed to cooking by sight. She removes the bones from the lamb, which is unusual in Rome.
2 tablespoons unsalted butter
1 tablespoon extra virgin olive oil
2 tablespoons chopped onion
3 tablespoons chopped prosciutto (about 1 slice; do not discard fat)
3 1/2 pounds (1,600 g) boneless leg of lamb, cut into 2-inch (5-cm) cubes
Coarse salt and freshly ground black pepper
1 tablespoon all-purpose flour
1 cup dry white wine
2 cups hot water, or as necessary
3 egg yolks
2 tablespoons chopped fresh parsley
1 teaspoon dried marjoram
3 tablespoons lemon juice
1. In a large skillet, heat the butter and oil and saute' the onion, prosciutto, and lamb over moderate heat until the prosciutto is browned, taking care not to burn the onion, about 20 minutes. Sprinkle with salt and pepper to taste, add the flour; cook, stirring, for 2 minutes.
2. Add the wine and allow to evaporate for 2 to 3 minutes, scraping up the particles of meat on the bottom of the skillet with a wooden spoon. Add enough hot water to the lamb almost to cover. Place a lid on the skillet and simmer for about 1 hour, adding more water if necessary. At the end of the cooking time there should be abundant pan juices, but they should not be watery. (Up to this point the lamb may be prepared in advance.)
3. Ten minutes before serving, beat the egg yolks lightly with a fork, adding the parsley, marjoram, and lemon juice while beating. Pour this over the hot lamb, mixing with a wooden spoon. Cook over lowest heat for about 5 minutes, until the egg yolks form a cream that veils the meat. (Take care that the heat is not too high, or the sauce will curdle.) Serve hot.