Make a shortcrust pastry from flour, butter, egg yolk, water and salt. Shape into a ball and chill for 1 hour.
In the meantime, fry the ham cubes briefly in a pan. Whisk eggs and sour cream, fold in cheese and ham cubes and season with salt and pepper.
Grease 4 tartlet molds (12cm). Divide the dough into 4 portions, roll out and line the molds with it. Spread the cheese mixture on top and then place the molds in the cold oven. Bake the quiches at 200 degrees for about 30 minutes. The cheese should be lightly browned.