For the dough, knead 200 g flour, 1 pinch of salt, 100 g butter in pieces, egg yolk and 3 tablespoons of cold water to a smooth shortcrust pastry. Wrap in foil and chill for about 30 minutes.
Clean and wash the leek and cut into fine rings. Heat 1 tablespoon of butter in a frying pan. Steam the leek for 3-4 minutes. Sprinkle with 1 tbsp. flour and sauté briefly. Add wine, bring to the boil. Stir in crème fraiche.
Simmer for about 5 minutes while stirring. Season to taste with salt and pepper.
Preheat oven (electric cooker: 200°C/circulating air: 175°C/gas: level 3). Grease six tartlet cups with removable base (approx. 12 cm Ø) and dust with flour. Roll out the dough on a little flour and cut out 6 circles (approx. 14 cm Ø).
Place in the moulds, press on the edge and prick the base several times with a fork. Pre-bake in a hot oven for about 15 minutes.
Cut 4 slices from the cheese. Crumble the remaining cheese and stir into the leek. Spread on the pre-baked bases. Cover each with 1 slice of cheese and bake at the same temperature for 15 minutes.
Possibly garnish with rosemary.