Mince the meat coarsely with the onion. Cut the bread into cubes and soak in a little water. Squeeze out the moisture, and mix the bread with the meat. Season with the salt and pepper and the finely chopped sage. Put into a loaf tin or casserole, and bake at 350°F, 180°C, gas mark 4 for one hour. Cool in the tin or casserole before turning out. Cut in slices to serve with salad, or use in sandwiches.