Clean the leek, cut in half lengthwise and wash. Cut leek into fine strips. Heat the oil in a pan and fry the ham. Add the leek and fry for 1-2 minutes. Remove from the heat, season with pepper and leave to cool. Stir sour cream until smooth, season with salt and pepper
Remove the dough from the packaging and unroll. Turn the dough sheet over onto a floured tea towel, carefully peel off the baking paper. Quarter the dough sheet into 4 rectangles (approx. 12 x 20 cm). Brush the quarter with approx. 1/2 of the sour cream, leaving approx. 1 cm of edge free. Spread the leek mixture on top, sprinkle with about 2/3 of the cheese. Fold the rectangles from the short side, press the edges firmly together
Place on a baking tray lined with baking paper and sprinkle with the remaining cheese. Bake in a preheated oven (electric cooker: 225 °C/ convection oven: 200 °C/ gas: see manufacturer) for 15-18 minutes. Serve with remaining sour cream