Preheat oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer). Whisk butter, 1 pinch of salt and 150 g sugar with the whisks of the mixer for 2-3 minutes until creamy. Separate 3 eggs.
Stir the egg yolks and 1 egg one after the other into the butter-sugar cream. Mix flour and baking powder, alternating with the lemonade.
Spread the dough on the paper baking cups. Bake in a hot oven for about 25 minutes.
Beat 3 egg whites until stiff, adding 150 g sugar. Pour the beaten egg whites into a piping bag (chill if necessary). After about 20 minutes baking time, remove muffins from the oven. Spray the beaten egg whites onto the muffins.
Continue baking for about 5 minutes. Remove and let cool on a cake rack.