Preparing the biscuit (sponge)

1. combine the sugar and eggs in the top part of a double boiler and whisk until warm; remove from the heat and continue beating until cooled and very light and foamy, about 10 minutes;
2. gently fold in the sifted flour, cornstarch and cocoa;
3. line a baking sheet with parchment paper; butter and flour a ring about 18 cm (7") in diameter and 7 cm (3") high; pour the batter into the ring and bake in a 180°C. (350°F.) for about 30 minutes; unmold and cool in the refrigerator. 

1. melt the chocolate in a double boiler;
2. add the egg yolk and lightly beaten cream; 
3. chill in the refrigerator for about 1 hour. 

1. beat the sugar with the orange juice and egg yolks in a double boiler until light and foamy; 
2. beat the cream until thickened but not stiff;
3. fold  the mandarine Napoléon and cream into mixture #1.

1. place the egg whites, sugar and cream of tartar in the double boiler; beat until stiff;
2. remove from the heat and continue beating. Fold into the mandarine mixture.

1. slice the sponge cake in equal layers;
2. place the baking ring on a baking sheet lined with parchment paper and a cardboard circle;
3. place one cake layer in the ring; top with chocolate mousse; repeat with all the layers; refrigerate for 1 hour;
4. pour the warm meringue/mandarine mixture over the cake; refrigerate for 12 hours;
5. remove the cake ring; cover the perimeter with cake crumbs; 
6. in a double boiler, melt the sugar and cobagel in the orange juice and white wine to form a jelly; wait for a few minutes and cover the harlequin cake with the jelly.