Place the puff pastry side by side on the work surface and allow to defrost. Clean, clean and slice the mushrooms. Halve bacon crosswise. Wash thyme, shake dry, remove leaves from stalks. Coarsely grate cheese
Whisk the egg yolk and milk together. Whip the puff pastry corners to the middle. Spread thinly with egg yolk. Spread two 1/2 slices of bacon and mushrooms on each pizza. Season with salt, pepper and thyme and sprinkle with cheese. Bake in the preheated oven (electric cooker: 225 °C/ convection oven: 200 °C/ gas: see manufacturer) for about 10 minutes