Preheat oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.

In a bowl, beat eggs and 2/3 cup sugar until light and fluffy.

Sift together potato flour, flour, and baking powder.

Add vanilla to the egg mixture and gently fold in the flour mixture.

Pour batter into prepared pans and bake for 15 minutes, or until a toothpick inserted into the center comes out clean.

Let cool in pans for 5 minutes before inverting onto a wire rack to cool completely.

In a bowl, beat egg yolks and 1/4 cup sugar until light.

Soften gelatin in cold water, then dissolve over hot water.

Add gelatin and vanilla to the yolk mixture.

Fold in whipped heavy cream.

Spread one cake layer with cream filling, top with the second layer, and frost the top and sides with remaining cream.

For the marzipan, combine almond paste, confectioners' sugar, green food coloring, and egg white until smooth.

Form into a ball, dust with confectioners' sugar, and wrap in wax paper. Chill for 1 hour.

Roll out marzipan into a 15-inch circle.

Carefully place marzipan over the cake, remove the wax paper, and press against the sides.

Trim excess marzipan and dust the top with confectioners' sugar.