Preheat the oven to 180 °C top and bottom heat (convection oven 150 °C). Grease a springform pan.
For the dough, quickly mix all ingredients until smooth and pour into the prepared pan.
For the topping, peel the rhubarb and cut into thin slices. Beat the egg whites with sugar until firm.
Scatter the rhubarb pieces evenly over the batter in the mold. Spread the snow over the top in large flakes.
Bake the cake in the hot oven for about 45 minutes.
Allow to set for another 5-10 minutes in the turned-off oven and then cool at room temperature.