Instructions: Rub the butter into the flour and custard powder until the mixture resembles breadcrumbs. Stir in the caster sugar and chopped walnuts. Press the mixture into the shallow, greased, 11-inch by 7-inch baking tin and bake at 325 degrees F., 160 degrees C., Gas Mark 3, for 30 minutes. Leave to cool in the tin. Cut into fingers while still slightly warm and leave until set.

To make the fudge topping, place the butter, soft brown sugar and cream in a saucepan. Boil for 3 minutes then beat until the mixture is the consistency of fudge. Pour quickly over the cooling biscuits and leave to cool completely.

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