For the cream puffs, boil 50 g butter, 1 pinch of salt, 125 ml milk and 125 ml water. Add 200 g flour at once. Stir with a wooden spoon until a white layer forms on the bottom of the pot and the dough comes off the bottom of the pot as a lump.
Put it in a mixing bowl. Leave to cool for about 10 minutes. Stir in eggs one after the other with the dough hooks of the hand mixer.
Pour the dough into a piping bag with a large perforated spout and squirt approx. 16 dough blobs onto a baking tray lined with baking paper. Stir egg yolk with 2 tbsp. water until smooth. Brush the dough with it. Bake in a preheated oven (electric cooker: 175 °C/ circulating air: 150 °C/ gas: see
manufacturer) bake for about 30 minutes until golden brown. Do not open the oven door. Let cool down on a cake rack.
In the meantime, clean and dice the mushrooms. Cut bacon into small strips. Grate cheese. Melt 20 g butter in a saucepan. Add 1 tablespoon of flour at a time while stirring.
Add 100 ml milk while stirring and stir until smooth. Stir in remaining milk and cheese. Let simmer for about 4 minutes at low heat. Season to taste with salt, pepper and nutmeg. Leave bacon in a pan for about 3 minutes until crispy.
Remove from the pan. Fry the mushrooms in hot frying fat until golden brown. Add to the sauce with the bacon. Season again with salt and pepper.
Cut off the lid of the cream puffs. Fill the cream puffs with the béchamel, place the lid on top and arrange on a plate. Garnish with Thai cress if necessary.