Step 1

Preheat oven to 200°C. Spray a round 22cm (base measurement) cake pan with oil. Line base and side with non-stick baking paper.

Step 2

Place butter and chocolate in a heatproof bowl over a saucepan half-filled with simmering water (make sure the bowl doesn't touch the water). Stir with a metal spoon until chocolate melts and mixture is smooth. Set aside for 5 minutes to cool slightly.

Step 3

Use an electric beater to beat egg yolks and sugar in a bowl until thick and pale. Add rind, juice and vanilla. Beat until combined. Stir in almond meal and chocolate mixture.

Step 4

Use a clean electric beater to beat egg whites in a clean, dry bowl until firm peaks form. Use a metal spoon to fold half of the egg white into lemon juice mixture until just combined. Fold in the remaining egg white until just combined. Pour into prepared pan. Bake for 10 minutes. Reduce oven to 150°C. Bake for a further 55-60 minutes or until a skewer inserted into the centre comes out clean. Set aside in the pan for 10 minutes to cool slightly. Turn out onto a wire rack to cool completely.

Step 5

Meanwhile, whisk mascarpone and cream in a bowl until well combined and thickened.

Step 6

Dust cake with icing sugar. Cut into slices and serve with mascarpone cream.