1. Combine flour, salt, lukewarm water, oil, and the egg yolk and knead to get a smooth dough. Brush the dough with a little additional olive oil and place it in a tight-sealing container. Let it rest at room temperature for about 30 minutes.

2. Preheat the oven to 230°C (450°F) fan-forced. Line two baking sheets with baking parchment and set aside. Peel the onions and cut them into thin rings.

3. Divide the dough into eight portions (or two portions for two large Flammkuchen). Roll out the dough portions very thinly on a lightly floured surface. If the dough does not want to comply, you can simply stretch it over the back of your hands, like you would do with pizza dough – this is often the most effective method. Place four dough circles on each baking sheet, spread the sour cream all the way to the edges of the dough, and distribute onion rings and diced ham evenly on top. Season with salt and pepper and bake the Flammkuchen for about 8-10 minutes until nicely browned around the edges. When using a convection oven, you can easily bake to baking sheets at the same time. Serve warm.