For Filling

• 2 tbsp all-purpose flour
• ½ cup whole milk
• 1 stick unsalted butter, at room temperature
• ½ cup sugar
• ½ tsp vanilla extract

For Sponge Cake

• 7 eggs, yolks and whites separated
• 1½ cups all-purpose flour
• 4 tbsp cornstarch
• 1½ cups sugar
• 1 tbsp baking powder
• 1 tsp salt
• ¾ cup cold water
• ½ cup canola oil

Equipment

• nonstick cooking spray
• "cream canoe" baking pan (4½" x 1¾" x 1½" wells)
• piping bag fitted with medium round tip or filling injector

Make Filling

1. In a small saucepan, heat the flour and milk over medium heat, stirring constantly
2. When the mixture becomes a paste (about 5 minutes), remove from heat and allow to cool for 1 minute
3. Using a stand mixer fitted with a paddle attachment, cream the butter, sugar, and vanilla until light and fluffy
4. Add the cooled milk mixture and beat for 5 minutes, until light & fluffy
5. Place a piece of plastic wrap directly onto the surface of the filling to prevent a skin from forming. Refrigerate while making the cakes

Make Cakes 

1. Preheat the oven to 350˚
2. Coat a canoe pan (you can use muffin tins as well) with nonstick cooking spray
3. Using a hand mixer, beat the egg whites until they reach stiff peaks, about 5 minutes. Set aside
4. Using a stand mixer fitted with a paddle attachment, combine the flour, cornstarch, sugar, baking powder, and salt in a large bowl. Whisk together or beat on low speed for a minute, until combined. Add oil, water, vanilla extract, and egg yolks. Beat on medium speed until smooth
5. Using a rubber spatula, gently scoop ⅓ of the egg whites into the batter and fold them in. Repeat the process until all of the whites have been added
6. Spoon the batter into the pan, filling the wells ⅔ full
7. Bake 8-12 minutes, or until cakes are golden brown and just starting to pull away from the sides of the pan
8. Cool cakes in the pan for 5 minutes, then gently remove from the pan using a rubber spatula. Allow them to cool on a rack, flat-side-down

Fill the Cakes

1. Use the pastry filler that comes with the pan (or a pastry bag fitted with a round tip) to fill cake with the cream
2. Hold a cake in your hand, upside-down, place the tip half way into the cake and squeeze gently to fill
3. Repeat this process in two other areas of the cake (to assure cream with every bite)
4. Keep in airtight container at room temperature for up to a week