Have room temperated butter in a bowl and blend till its white with a blender. While blending butter, put dried cep mushroom in the food processor and make cep mushroom flour.
Tear the lemon skin (not the white part) and press the lemon juice. Add the cep mushroom flour, chopped garlic, lemon skin and lemon juice to the butter. Blend well and add salt and pepper.

Boil the beans with salt for 3 minutes. Cool directly in running cold water.

Take the beans out of the water and dry on paper towels. Chop shallots and mix with the beans in a bowl. Cut the shell along the crab claws so the meat is in the smooth part of the shell. Add the beans and shallots, add a bit of mushroom butter and broil them on high heat until the butter melts and the claws are tanned on top. Mix the beans and shallots with mayonnaise dressing.

Serve the crab with bean salad.