Transfer the flour on your worktop and use the bowl to make a well in the middle. Fill it with the mushroom powder, the sugar, the salt, the water, the olive oil and the egg yolk. Then mix it and knead it into a nice ball of dough. If you feel like the dough is to soft add a little bit more flour. Now let it rest in your fridge for at least 30 minutes. After that flour your worktop and roll out the dough until it’s 2 to 3 millimeters thin. Then cut it with a small round cutter. Now spray a little bit of oil spray on some small tartelettes molds and place the dough on 2/3 of the molds. Shape them and then place another mold on top. After place another on top. In total you can stack two to three tartelettes. Then bake them at 170 degrees Celsius for around 20 minutes. Now when still hot remove the tartelettes from the mold to prevent them from breaking. Keep them dry and covered.