For the sauce: Saute mushroom in ½ oz melted butter on medium for 5 minutes. Add shallots and stir.
Add wine cream,and lemon. Let this cook on medium for 5-10 minutes and reduce the heat to low and add watercress. When it is thick add salt and pepper.
For the shrimp: Saute the shrimp in 6-8 tablespoons of butter in a separate pan for 3-5 minutes or until opaque and cooked through. Cook on one side for 2 minutes and the other side for 2 minutes.
To serve: Put the shrimp on a plate and pour the watercress sauce on top.