Clean the leek, cut in half lengthwise and wash. Grease a baking tray (approx. 42 x 29 cm). Put the contents of the bags of the basic mixture into a bowl and add 1/4 litre of lukewarm water. Knead with the dough hooks of the hand mixer to a smooth dough until the dough comes off the bowl rim. Then knead briefly with your hands. Roll out the dough on a floured work surface to a rectangle (approx. 48 x 35 cm), place on the baking tray and prick several times with a fork.
Spread tomato puree on it and drizzle oil over it. Pre-bake in the preheated oven (electric cooker: 200 °C/ gas: level 3) for approx. 20 minutes. Grate cheese on the coarse side of a household grater. Wash, clean and slice the tomatoes. Cover pre-baked pizza with tomato slices and sprinkle with cheese. Bake at the same temperature for another 15-20 minutes