Clean, wash and cut the rhubarb into small pieces. Put the fat, salt, vanilla sugar and 150 g sugar into a mixing bowl, whisk with the whisk of the hand mixer until foamy.
Separate two eggs. Stir in 2 eggs and 2 egg yolks one after the other. Mix flour (up to 1 tablespoon) and baking powder and stir in alternately with the milk. Turn rhubarb in the rest of the flour and fold into the dough.
Place 2 paper cups in each of the 12 wells of a muffin tin. Spread the dough evenly with a tablespoon. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: not suitable/ gas: level 3) for 30-35 minutes.
Meanwhile beat 2 egg whites until stiff. Finally, pour in 80 g sugar. Pour the beaten egg whites into a piping bag with a perforated spout. 5 minutes before the end of the baking time, spray the muffins with sugar and finish baking.
Remove from the oven and leave to cool on a grill. Serve dusted with icing sugar.