Prepare a yeast dough from the yeast, water, sugar, flour, salt and oil. Let the dough rise for about 30 minutes.
Knead again and divide into 6 pieces. Shape each into a roll and use the rolling pin to make a triangle (as large as possible). Sprinkle each triangle with cheese. Roll up from the broad side towards the tip. Place the seams down on a parchment-lined baking sheet. Let rise again for about 45 minutes.
Score the croissants lengthways to reveal a layer of cheese. Let rise again for 15 minutes.
Preheat the oven to 220 ° C and bake for 20 minutes.
Variations that we tried: sprinkle chopped ham, or smoked ham or chopped salami with the cheese on the croissants.