Melt butter in pan and add flour. Stir together and heat for 2 minutes. Stir in milk and cream and continue to stir until milk/cream mixture is totally incorporated and mixture is thick. Add 1 tsp. salt (more to taste) and cayenne and fresh nutmeg. Cover with saran until ready to add lobster.
When ready to serve, heat sauce, add chopped pieces of lobster (prefer tails) and add juice of ½ lemon and 1 ½ TBS. sherry (don’t boil once sherry is added).
Taste again just before serving and add more salt, lemon, or sherry as needed.
If too thick, add an extra 1-2 cups of milk as needed.