Crumble yeast in 1⁄4 l lukewarm water and dissolve in it with 1 tablespoon of sugar while stirring. Leave to stand for approx. 5 minutes until the yeast water throws bubbles.
Put 400 g flour in a large bowl and press a depression in the middle. Pour yeast water into the hollow. Mix with some flour from the edge to a pre-dough. Cover and leave to rise in a warm place for about 15 minutes.
Add 1 tsp salt and 2 tbsp oil. Knead with the dough hooks of the mixer for about 5 minutes to a smooth dough. Cover and leave to rise in a warm place for about 30 minutes.
Peel onions and cut them into fine rings. Cut mozzarella into thin slices. Finely slice parmesan.
Preheat oven (electric cooker: 250 °C/circulating air: 225 °C/gas: see manufacturer). Line baking tray with baking paper. Knead yeast dough well on a floured work surface. Cut dough in half and roll out to a rectangle (approx. 39 x 26 cm).
Place the pastry base on the baking tray. Cover with mozzarella, season with salt and pepper. Place 2nd base on top. Spread onions on it, sprinkle with 2 tablespoons of oil. Sprinkle with parmesan and season with pepper.
Bake in a hot oven on the lowest shelf for 20-25 minutes. Wash the marjoram and remove the leaves. Sprinkle over the pizza about 3 minutes before the end of the baking time.