Over a low heat, sweat the onion in a covered pan with a splash of olive oil until really soft. Remove the lid, increase the heat and add the chilli, tomatoes and a wine glass of water. Season lightly and cook gently for 30 minutes, then break up the tomatoes.
Whiz the bread to breadcrumbs in a food processor. In a large bowl, mix the meats with the nutmeg, the herbs, the zest, the egg yolk and the breadcrumbs. Season and shape into little balls the size of gobstoppers.
Add 3–4 tablespoons of olive oil to a hot pan. Brown the meatballs all over, but be careful not to break them up. Then add them to the pan with the tomato sauce, stir carefully, cover, and braise gently for 45 minutes or so until cooked. Serve each portion scattered with a few raw peas, pecorino shavings and marjoram, if using.