Take the puff pastry out of the refrigerator 5-10 minutes before use. Clean, wash and cut the leek into rings. Heat the butter and sauté the leek for about 4 minutes. Wash the cress, shake dry, pluck the leaves from the stalks and chop coarsely except for a little to garnish.
Roll out the puff pastry and cut into 15 squares (approx. 8 x 8 cm). Cut cheese into 30 thin slices. Whisk egg and spread thinly on squares. Spread the puff pastry squares on a baking tray lined with baking paper. Spread a thin layer of mustard on the squares in the middle. Spread leek, cress and 2 slices of cheese on each
Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: see manufacturer) on the lower shelf for about 20 minutes until the puff pastry has risen and is golden brown. Garnish with cress