Boston Baked Beans

• 2 lb/1 kg dried haricot beans
• 2 teaspoons mustard powder

Soak the beans overnight in cold water and drain them well. Mix the mustard, salt and pepper in an oven-proof casserole. Stir in the beans and cover with water. Add the tomato purée, syrup, treacle and brown sugar. Peel and quarter the onions and add to the casserole. Cover tightly and bake at 275°F/140°C/Gas Mark 1 for 8 hours, adding a little water if necessary so the beans do not dry out. So