Finely dice the vegetable onion and garlic and sauté in the butter until translucent. Cut the mushrooms into leaves and cook for 10 minutes. Dust with flour, pour stock and cook for 15 minutes. Add the cream, processed cheese and white wine and bring to the boil. Season with salt and pepper.
Pour the soup into 4 ovenproof soup cups and brush the rim of the cups with whisked egg yolk.
Cut 4 circles out of the puff pastry, the circumference of which is slightly larger than that of the cups. Place the pastry lid on the cups and press down on the edge. Brush with egg yolk and sprinkle with sesame seeds. Bake in the preheated oven for 20 minutes at 200 g, until the puff pastry has risen nicely.