For the dough baking mix and 340 ml lukewarm water in a bowl. Knead to a smooth dough with the dough hooks of the hand mixer. Cover the dough and let it rise in a warm place for about 20 minutes.
Peel the onion and slice into rings on the vegetable slicer. Roll out bread dough on a floured work surface in an oval shape (34 x 25 cm). Place on a baking tray lined with baking paper. Spread onion rings on the dough.
Cover the dough with a second baking tray and let it rise again for about 15 minutes. Cut off the rind of the cheese slices. Put the cheese on the bread. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for 30-35 minutes.
Season with pepper.