Paper Wrapped Sponge Cake

1.Cut six pieces of parchment paper into 7 inch squares with four slits on each side. Nest the parchment squares into a muffin tin, forming a liner. Preheat oven to 350 degrees F.
2.Combine flour, cornstarch, and baking powder in a mixing bowl. Separate the eggs from yolks and whites.
3.Add the egg yolks and 1/4 cup of sugar to the bowl of a stand mixer. With the whisk attachment, beat on medium high speed until the mixture is a very pale yellow and has increased in volume by double, about 4 minutes. Scrape down the bowl, add oil and beat until smooth, another 1 minute.
4.Add milk and vanilla, and beat again for 30 seconds. Transfer the egg yolk mixture to a large mixing bowl. Clean both the whisk attachment and bowl of the mixer with soap and water. Return to the stand mixer.
5.Add egg whites, whisk on medium speed for 1 minute until frothy. Sprinkle cream of tartar over the whites and whisk for another 2 to 3 minutes until soft peaks form. Turn the speed up to medium high and start adding the remaining 1/4 cup sugar 1 tablespoon at a time, beating until stiff peaks form, 1 to 2 more minutes.
6.Sift the flour mixture into the egg yolk mixture. Stir with a spatula until smooth. Add the egg whites and very gently fold into the batter until no streaks remain.
7.Divide the batter evenly between the cake liners. Bake for 20 to 22 minutes until golden and puffy, and a skewer inserted in the center comes out clean. Remove from oven and immediately take the cakes out of the tin and turn them onto their sides on a clean kitchen towel, this helps keep their shape as they cool. Let the cakes cool to room temperature and enjoy.