Clean the mushroom and chop into fine chunks.
Finely chop the shallot, pickles, capers and waterpepper.
Add the mushroom, the shallot, pickles, capers, and waterpepper to a large mixing bowl.
Add the remaining ingredients and mix well. Add salt to taste and more tabasco if needed.
Press the mixtures in two large cups or ramekins.
Flip the cups or ramekins over on a serving plate while tapping on the top to release the tartar.
Top each tartar with a raw egg yolk.