Preheat oven to 300F (150C).

Grease and flour two 9-inch round cake pans.

Line the pans with wax paper, then grease the wax paper and dust with flour.

Melt the chocolate in a double boiler, then let it cool.

Cream butter and sugar in a mixer until pale and bubbly.

Add egg yolks one at a time, beating well after each addition.

Beat in the cooled chocolate and orange juice.

Mix in cocoa powder, cognac, flour, lemon rind, orange rind, vanilla extract, and ground almonds.

Beat egg whites until stiff peaks form.

Fold half of the egg whites into the batter.

Fold in the remaining egg whites gently.

Divide the batter evenly between the two pans.

Smooth the tops of the batter.

Bake for 50 minutes.

Let the cakes cool in the pans for 10 minutes.

Invert the cakes onto wire racks to cool completely.

Refrigerate before serving.

Dust with cocoa powder or confectioners' sugar before serving.