Preheat the oven to 190 °C.
In a large bowl, whip the egg whites with an electric whisk on medium speed. When the egg whites are almost completely whipped, add the sugar a little at a time, continuing to whip on high. Don’t forget… whip the egg whites with the sugar until soft peaks form.
Add the flour to another smaller bowl. Add a tablespoon of whipped egg whites and mix. Repeat with 2 to 3 more tablespoons of egg whites. In this way, you will obtain a kind of batter that will be easy to mix with the egg whites.
Take back the bowl with the whipped egg whites. Add the vanilla extract, baking powder, and flour batter. Incorporate everything well, mixing slowly from bottom up so as not to disassemble the egg whites.
Grease a 24 cm diameter cake tin with a bit of butter and flour it well. I prefer to use a spring form pan, but it’s not essential because the cake will come away perfectly from the sides during cooking. Transfer the mixture to the springform pan and level the surface with a spatula or spoon.
Bake for 35–40 minutes at 190 °C, until lightly browned. The cake will be cooked when a toothpick inserted in the center comes out clean and dry. If during cooking you notice that the cake takes on too much color, cover it with aluminum foil until the end of cooking.
Remove the cake from the oven and let it cool for about 1 hour.
Immediately invert the pan and allow the cake to cool completely, in this way the cake will remain moist and soft inside.
When the cake has cooled, cut it in half horizontally. Remove the top half, spread the hazelnut spread on the bottom halves, and reseal with the other half. Sprinkle with powdered sugar and slice.
Your Vanilla Egg White Cake is ready to be enjoyed!