How to Make It
Preheat the oven to 350°. Butter an 8-inch square cake pan and line the bottom with parchment or wax paper. Butter the paper.
In a standing electric mixer fitted with a whisk, beat the egg yolks with the whole egg and sugar at medium speed until pale yellow, light and fluffy, about 15 minutes.
Sift together the flour and cornstarch. Gradually beat the flour mixture into the eggs on low speed, by the handful, adding more only when the previous handful has been absorbed. Increase the speed to medium and pour in the melted butter in three batches. Before the last addition of butter is completely incorporated into the batter, turn off the machine and fold with a large rubber spatula using gentle, circular motions until just combined.
Scrape the batter into the prepared pan. Using two sheets of aluminum foil, wrap the pan completely top and bottom. Fold the foil loosely at the top, to allow room for expansion. Bake in the center of the oven for 40 minutes, or until the cake has risen and springs back when lightly pressed. Immediately unmold the cake onto a plate, peel off the parchment paper and turn the cake right side up. Cool to room temperature. Cut the cake in half and then cut each half into 5 slices. Serve with the Wild Berry Compote.