If you have a whole crab open it up, remove the gray gill like structures and put all the white and brown meat in a bowl and set aside.

Finely chop two cloves of garlic and thinly slice 3 medium sized button mushrooms. Meanwhile melt the butter in a saucepan on a low heat. (Do not fry or boil this sauce at any stage. You just want things to soften not cook hard)

Add the garlic, mushrooms and crabmeat and just bring it to the point where the butter is beginning to bubble.
Add a dash of white wine. (Not too much you don't want the sauce swimming). Keep stirring so it doesn't get too hot until the mushrooms have just softened a little.

Add the cream and the pepper and just bring to a simmer stirring all the time. The moment it does add your cooked pasta and serve with some parmesan flakes. The whole cooking process takes just 5 minutes so plan your tagliatelle accordingly.