Line a baking sheet with parchment paper. Preheat oven at 190°C/374°F.
Combine all ● ingredients and sift into a bowl. Mix in the egg.
Whisk with a hand mixer until thick.
Rinse the hand mixer. Add egg white into a separate bowl, then add granulated sugar in small batches to make a meringue.
Melt butter in a microwave or a double broiler. Mix into the batter from Step 3.
Add a scoop of meringue from Step 4 into the batter from Step 5.
Pour the whole batter from Step 6 into the bowl of meringue.
Mix everything together until even to finish the batter.
Pour into the baking sheet. Smooth out using a cake knife or a bench scraper.
Bake in the oven for approx. 12 minutes.
When done, cool on a rack.
When it's cooled down, cut into desired shapes using a mold like cookie cutters to use as a base for cakes.
Story Behind this Recipe
I usually make mousse quite frequently during the summer. Because it's too much trouble to bake base cakes each times, I came up with this recipe to make a lot at once and to freeze for later use.
If you whisk the egg white too much, it becomes difficult to mix. If it's too runny, the batter doesn't turn out well. Just make sure to stop whisking when it forms stiff peaks. You could freeze this cake after it's baked. Wrap with plastic wrap and freeze in a ziplock bag. Make sure to use it up quickly.