Work the flour, oil, water and salt into a smooth, non-sticky dough. If the dough is too crumbly, add a little more oil and water. The sparkling water makes the dough a little looser. If the dough sticks, add a little flour. Shape the dough into a ball and place in cling film in the refrigerator.
Preheat the oven to approx. 220 ° C convection or 230 ° C top / bottom heat.
Mix the crème fraîche or sour cream with the cream or milk. Put the cream in the fridge.
To cover, take the dough out of the refrigerator and roll it out to the size of the baking sheet about 3 - 5 mm thick, place it on a greased baking sheet or a baking sheet lined with baking paper (pizza oven or baking stone are of course also possible, but only then pour in). Spread the cream evenly on the dough with a spoon and cover.
Salty topping: Dice the onions or cut into half rings, cut the bacon into fine cubes of the same size (Katenschinken is already diced and has less fat than bacon). Spread the bacon and onions evenly on the cream.
Sweet topping: peel the apples and cut into thin slices. Pour some lemon juice over the slices. Place the apple slices side by side on the dough and sprinkle with the flaked almonds. Then sprinkle with cinnamon sugar.
Bake the dough in the oven for approx. 10-15 minutes until the edge is brown. Then divide the finished tarte flambée and serve with Federweißer, white wine or a pilsner.