1.Preheat oven to 200°C/400°F.
2.Trim excess fat from lamb. Pierce lamb in several places with sharp knife; press sliced garlic and a little of the rosemary firmly into cuts. Rub salt and pepper over lamb.
3.Heat butter in large flameproof baking dish on stove top; cook onion and crushed garlic, stirring, until onion browns slightly. Stir in undrained tomatoes, purée, stock, beans and remaining rosemary; bring to the boil then remove from heat.
4.Place lamb, pierced-side down, on bean mixture, cover; transfer to oven. Cook 1 hour. Uncover, turn lamb carefully; cook, brushing occasionally with tomato mixture, about 1 hour or until lamb is cooked as desired.
Slow cooker: suitable to the end of recipe. Pressure cooker: suitable to the end of recipe. Suitable to freeze at the end of recipe. You can use canned cannellini, navy, great northern or butter beans in this recipe.Note