Work the butter into the flour, then add the egg and pour the water little by little while kneading to obtain a smooth dough.
Wrap in plastic film and let rest in the refrigerator for at least 2 hours.
Roll out the dough to a thickness of 3-4 mm and bake for 12-15 minutes in a 150°C oven until it is cooked through and dry.
If it begins to colour too quickly, lower the temperature.
Let cool and reduce to crumbs.
Wash and cut 300 g of button mushrooms into strips.
Put them in a saucepan with 1 liter of water, bring to a boil and cook over low heat for about 10-15 minutes.
Allow to cool, and filter the liquid obtained by carefully squeezing the mushrooms to extract all the juice.
Season with salt, pepper and nutmeg.
Mix 1.5 g of agar-agar powder with 1.5 g of pectin starch.
Bring 250 ml of mushroom juice to a boil and pour in the powders while whisking.
Cook for 1 minute while continuing to stir. Set aside.
Saute the mushroom separately over high heat.
Season, then transfer to a tray to cool down.
Chop coarsely with a knife, reserving a few nice mushrooms for decoration.
Chop the parsley.
Transfer the filling to a bowl.
Moinsten with 300 g of jelly and add a little chopped parsley.
Combine all ingredients to obtain a homogenous texture.
Fill a piping bag fitted with a plain tip and set aside.
Pipe 50 g of cheesecake mixture onto the base. Spoon the mushroom filling on top.
Before the jelly sets completely, top with one or two whole cooked mushrooms to decorate.