Heat oysters in liquor over low heat until edges curl. Drain, saving liquor. Melt 1 tbs butter, blend in flour, add milk gradually, stirring constantly. Bring to boiling and cook 1 minute. Add cream, shallots, parsley, salt and pepper. Warm mushrooms in remaining butter until heated but not brown. Combine mushrooms, oysters, and oyster liquor to cream sauce. Serve immediately.