Start by melting butter in a saucepan. Make sure the heat is medium-low.
Sauté garlic and shallot, or onion in the pan for 2 to 3 minutes.
Pour heavy cream and Dijon mustard into the pan. Then simmer the sauce until it becomes slightly thick.
Now gently fold in the crabmeat. Make sure the lumps don't break.
Next, add Old Bay seasoning, lemon juice, salt, and pepper.
Let the sauce simmer for 5 to 7 minutes over low heat. Also, stir it occasionally.
Now, garnish the sauce with some chopped parsley, and you are done.