150 g (5 oz) unsalted butter, softened, plus extra for greasing
125 g (4 oz) golden caster sugar
100 g (3 1/2 oz) self-raising flour, sifted
1 teaspoon baking powder
50 g (2 oz) ground hazelnuts
2 large eggs, lightly beaten
2 teaspoons finely grated orange rind, plus extra to decorate
1 teaspoon orange extract
125 g (4 oz) ready-made crumble mix
mascarpone cheese, to serve
Grease a 23 cm (9 inch) square cake tin and line with nonstick baking paper.
Place all of the ingredients except the crumble mix in a large bowl and beat together with a hand-held electric whisk until pale and creamy. Spoon the mixture into the prepared tin and sprinkle over the crumble mix.
Bake in a preheated oven, 200°C (400°F), Gas Mark 6, for 22 minutes, or until golden and firm to the touch. Turn out of the tin on to a wire rack and peel away the lining paper.
Serve warm or cold with mascarpone, decorated with orange rind.