Rub the flour and 100g of butter together, and then use 3-4 tablespoons of cold water to bind the mixture together into a pastry dough. Wrap it in foil and put it in a cool place for at least an hour.
Peel the onions and slice them into thin rings. Clean the mushrooms, dry them and then slice them finely. Cut the speck and bacon into small dice. Put the rest of the butter into a pan and sweat the onion rings in it. Preheat the oven to 200C (180C for fan-assisted ovens).
Grease a loose bottomed 26cm flan tin (or line it with baking parchment). Roll out the pastry and line the tin with it, making sure the dough comes up high on the sides. Mix the onions, mushrooms, bacon and caraway seeds together, and spread it over the pastry base.
Mix the sour cream, cheese, eggs, salt, pepper together and spread over the onion mix. Cook for 40 minutes until the top is brown and the pastry is crisp.
For the schinkenspeck, you can use the Italian version if you can’t get the German one or you can just use streaky bacon.
For the cooked bacon, normally I use whatever bacon is around the house, anything from streaky to back bacon works fine provided you cook it first.
Buy the Emmental cheese ready grated if you can.
For the caraway seeds, if you can’t get ground ones and you don’t have a pestle and mortar or grinder, just use whole caraway seeds.