For the rhubarb sheet cake, first line a baking tray with baking paper. Preheat the oven to 180 °C.
Peel the rhubarb, cut away the ends and dice the rest.
Mix flour, baking powder, baking soda and almonds.
Beat sugar, vanilla sugar and butter until fluffy. Beat in eggs a little at a time. Fold in the flour mixture. Spread on the baking sheet and top with the rhubarb. Sprinkle sugar and flaked almonds on top. Place in the oven for about 25-30 minutes.
While the cake is in the oven, beat the egg whites until stiff peaks form. Add powdered sugar and beat until a firm mixture forms. Just before the end of the baking time, spread on the rhubarb sheet cake and finish baking with the snow topping.
Preparation Tip:
You can also bake the rhubarb sheet cake without the snow cover.