Make the cake: Butter and flour a square baking pan, turn it upside down, and tap it to remove excess flour. Blend the marzipan, orange zest, and orange juice until a smooth cream forms.

In a large bowl, whisk together the soft butter with the orange zest and sugar. Whisk in the eggs, one at the time. Incorporate the flour and chopped orange peel. Mix well until homogenized. Pour in the almond cream and Grand Marnier, then mix well again until smooth.

Bake the cake: Transfer the mixture into the prepared pan. Smooth the top of the cake with the back of a spoon. Bake for about 25 minutes on the bottom rack of the oven. When cooked, unmold the cake on a wire cooling rack and allow cooling. When cold, dust the cake with icing sugar.

Finish the cake: Place the milk in a saucepan and bring to a boil. Off the heat, whisk in the dark chocolate until melted. Whisk in the cocoa powder until smooth.

Serve the cake: Cut the cake and plate it. Decorate each slice with chocolate sauce, candied orange skin and toasted almonds.