Sweet Potato and Caramel Cheesecake

Preheat oven to 180 C / Gas 4. Mix together digestive biscuit crumbs, 4 tablespoons sugar and 4 tablespoons melted butter. Press mixture into the bottom of a 23cm springform tin. Bake 10 minutes. Cool. Don't turn the oven off.

Place potatoes in a baking dish. Bake until a knife inserted in centre goes through easily, about 1 hour. Don't turn oven off. Cool sweet potatoes enough to handle, peel and puree.

Transfer 375g sweet potato puree to a large bowl. Add cream cheese, 175g sugar, soured cream and 4 tablespoons double cream; beat until smooth. Beat in eggs one at a time, blending well after each. Pour filling into base.

Bake until skewer inserted in centre comes out clean, 1 hour. Turn off the oven. Let cake stand 1 hour in oven with door ajar.

Combine brown sugar and 50g butter in a heavy small saucepan. Stir over low heat until sugar dissolves. Increase heat and bring to the boil. Mix in 4 tablespoons cream, then pecans. Pour hot topping over cheesecake. Refrigerate.