Sift the flour and salt into a bowl. Knead in the butter until everything is a crumbly mass. Add the water and mix everything into a dough.
Roll out the dough on a lightly floured work surface. Use a round cookie cutter about 7 cm in diameter to cut out 12 small cakes and use them to line a muffin tin or cake molds.
For the filling, whisk the beaten egg, cream, cheese and onions in a measuring cup. Season to taste with salt and cayenne pepper.
Spread the filling evenly on the dough and bake everything in the preheated oven at 180 ° C (gas: level 2) for about 20 to 25 minutes until the filling is firm. You can serve the cheese and onion cakes either warm or cold.
Variation: You can top each cake with a tomato slice before baking.
Tip: It`s even faster if you use 175 g ready-made shortcrust pastry instead of making the dough yourself.