Raspberry Buttermilk Sponge Cake

Preheat oven to 400F/200C.
First, separate the egg yolk from your egg whites into two mixing bowls. Complete until you reach 1/3 cup (80g) of egg whites. Set aside.
In the first mixing bowl, whip the egg whites with the salt until stiff peaks. Set aside.
In the second mixing bowl, whip together the egg yolk and sugar until light and fluffy on a medium high speed for 2 minutes. Then, add the softened butter, buttermilk and the vanilla extract. Beat for another minute. Slowly add the flour, baking powder and baking soda. Mix until combined. IMPORTANT: Do not over mix the batter. Then, carefully fold the egg whites.
Place your Tender Heart Flexipan® Mold on the top of your Medium Perforated Baking Sheet.
Gently pour over the preparation and flatten with your spatula. Sprinkle the Vanilla Sugar on top.
Bake for 10 minutes at 400F/200C. Then, quickly remove your cake from the oven, scatter your raspberries and bake for another 15min. (Every oven heats differently, monitor your cake from 12min). It is ready when the toothpick inserted comes out clean.
Once your cake is out of the oven, let it completely cool down before unmolding. Then, Serve and Enjoy! Bon Appétit!
N.B. If baked in a regular 9" mold, the raspberries do stay on top. However, in the Tender Heart mold they sink down, because the batter is thicker. Therefore just remember to keep some raspberries to add on top.