Preheat the oven to 180°C/160°C fan oven/Gas Mark 4.To make the base, using a food processor, whisk the eggs and the caster sugar together on high until the mixture has doubled in volume and is very thick. (If you do not have a food mixer, place the eggs and sugar in a large heatproof bowl and whisk using an electric whisk or large balloon whisk over a pan of simmering water until thick. Remove from the heat and whisk until cool.)

Sift the flour with the cocoa powder and lightly fold into the eggs, then add the butter, folding until just combined. Do not over mix as the air will be knocked out of the mixture and the resulting cake will be flat.

Grease a 25cm (10 in) loose-bottomed cake tin and baseline with non-stick baking parchment. Pour the mixture into the tin and bake for 25 to 30 minutes. Cool for 10 minutes before turning out on to a wire rack. Drizzle with Grand Marnier, then allow to cool. Return, upside down, to the clean tin and press firmly into the base.

For the chocolate and orange truffle mixture, melt the chocolate in a heatproof bowl with half the cream, over a pan of simmering water. When melted, stir until smooth, remove from the heat and leave to cool.

Whisk the remaining cream to soft peaks. Using an electric whisk, beat the egg yolks and sugar together until pale and fluffy. Beat the egg mixture into the cooled chocolate, then fold the chocolate mixture into the whipped cream with the orange rind. Immediately pour this over the cake in the cake tin and chill for at least 2 to 4 hours or until the truffle mixture is set firm.The torte is best left overnight before serving.

To serve, remove the torte from the tin and dust with cocoa powder. Cut into portions and decorate with caramelised physalis.

For the physalis, fold back the dried 'petals' of the physalis, exposing the orange fruit and set aside. Place the caster sugar in a small heavy-based pan, add 6 tablespoons of water, dissolve over a gentle heat, bring to the boil and bubble until a rich caramel colour. Dip the base of the pan in cold water, then immediately dip the physalis into the caramel. Place on an oiled baking sheet and leave to set in a dry atmosphere for 3 hours.

Freezing: Complete recipe to end of step 5, wrap and freeze.

To use: Thaw at cool room temperature overnight. Complete recipe.