Sift the flour into a suitable bowl, make a hollow in the center. Melt the yeast in a little bit of water, add sugar, pour into the hollow and stir with a little bit of flour. Cover and let it rise for 10 minutes. Add the salt on the side and knead until smooth, adding the remaining water, egg yolks and melted lard with the dough hooks of the mixer. Place dough in a floured large baking bowl and rise with lid closed until doubled in volume.
Knead again briefly and roll out on floured surface, spread out a baking sheet with it, pushing up a 2 cm high edge, rise repeatedly for 15 min.
For the topping, fry the bacon cubes in a little lard, remove the bacon. In the frying fat, sauté the diced onions until translucent (do not let them turn brown!). Cool the onions, mix with 2/3 of the bacon cubes, season with salt and season with pepper (lots of black pepper!). Spread the amount evenly on the dough.
For the glaze, mix the eggs with the sour whipped cream, season with salt, season with pepper and spread evenly on the onions, sprinkle the remaining bacon cubes on top.
Bake the onion tart in a heated oven at 200 °C for about 45 minutes until golden brown.
Use ready-made “pizza dough” from the refrigerated counter (32 cm diameter, rolled up), in Switzerland sold as “cake dough”. In a 30 cm tart pan with approx. 2/3