I'd never made sponge cake, and I'd never used marzipan or almond paste. I decided to conquer (or at least make a brave attempt) both at the same time, making Sprinkle Bakes Potato Petit Fours for St. Patty's Day. Unfortunately, mine turned out remarkably potato-like in appearance but rather dismal in taste.
Potato Petit Fours
3 egg yolks
4 egg whites
1/4 cup fine granulated sugar, divided
1/2 cup cornstarch
2 Tbsp. flour
1 1/2 cups buttercream
1 1/2 cups your choice fruit jam
1 1/2 lbs. marzipan or almond paste
Cocoa powder for dusting
Preheat oven to 375ºF. Line two baking sheets with parchment paper.
Place egg yolks in a bowl and beat in 1 tablespoon of the sugar. Mix until frothy and lightened, and set aside. Beat egg whites in a separate large bowl. Gradually add remaining sugar and beat until meringue is stiff and dry.
Sift corn starch over meringues and fold in with a rubber spatula. Add beaten yolks and fold again, being very careful to not deflate the batter. Finally, fold in the flour.
Spoon mixture into a pastry bag fitted with a large plain tip and pipe 1 1/2-inch mounds spaced well apart onto the baking sheet. Bake for 6-10 minutes with the oven door slightly cracked. (You can use a spoon to prop the oven door open slightly, but remember the spoon will be hot!) When lightly brown, remove from oven and allow to cool completely.
Pipe buttercream between two same-sized sponge rounds. If using jam, use a sharp knife to make a small hollow in the bottoms of the cakes. Spoon in the jam and sandwich sponge rounds together.
Roll out marzipan or almond paste to 1/8-inch thickness -use a little confectioners' sugar to flour the work surface and rolling pin if paste sticks. Cut into squares and use to cover the potatoes. If paste doesn't stick to the cake, brush a little melted jelly over the surface. Make a few indentations to represent "eyes." Use a fork tine to further pock-mark the potato.
Roll the cakes in cocoa powder. Shake off excess and place in paper liners, brown paper bags or wrap in foil to mimic a baked potato.