Génoise: Preheat oven to 350 degrees F. Butter and flour an 8-inch cake pan.
Into a small bowl sift together flour, cocoa powder, cornstarch and baking soda.
In a large metal bowl set over barely simmering water, whisk eggs and sugar with a handheld electric beater or by hand with a balloon whisk until thick, foamy and tripled in volume. Mixture should form a ribbon when beaters are lifted. This may take up to 10 minutes. Watch the simmering water to make sure that the mixture does not get too hot and curdle the eggs.
Remove from heat and gently fold in the flour mixture until just combined. Fold in melted butter and pour into cake pan. Bake 20 minutes until cake is springy to touch. Cool in pan 10 minutes on a cake rack, turn out and cool completely.
Make a syrup by combining the 1/4 cup of sugar with the 1/2 cup water in a small sauce pan. Bring to a boil stirring constantly. Stir in the liquer and remove from the heat. Once it is completely cool, handle the cake carefully and brush it over both sides.
Ganache: In a small saucepan bring cream to a boil over high heat. Remove from heat and whisk in chocolate. Let cool, stirring occasionally, until thickened, but still pourable.
Assembly: Halve cake crosswise. On a cake rack set over a baking sheet, cover bottom cake layer with raspberry filling and replace top layer. Over center of cake pour ganache and smooth over top and sides with a palette knife until evenly coated. Let icing set, about 1 hour. To decorate, pipe whipped cream as desired, arrange raspberries and mint and dust with powdered sugar as desired.
Yield: 10 servings