Using a coffee grinder, grind the oat flakes into flour.

Separate the egg yolks and whites, and place them in separate bowls.

Place the egg yolks, vanilla sugar, and sweetener in a large bowl.

Beat with a mixer until smooth.

Add a little salt to the egg whites and beat well until stiff peaks form.

Gradually add the protein foam to the sweet egg yolk mixture.

Then sift the oat flour and gradually pour it into the mixture. Mix. The result will be a viscous, not very thick sponge cake dough.

Pour into a round baking pan (14 cm in diameter). But first, grease it well with a non-stick mixture of lard, flour, and vegetable oil. Alternatively, you can line it with oiled baking paper. Place the pan in an oven preheated to 175°C for about 35 (maximum 40) minutes.

The sponge cake is ready.

Transfer it to a wire rack to cool.

When it has cooled, cut it into two equal pieces and form the desired cake or pastry.