This is a classic rendition of parsley sauce that balances the strong herbal flavor of parsley with butter and cream, amp'd up with a little mustard powder. Great on fish, poultry, rabbit or pork loin.
Heat the butter in a small pot over medium heat. When it's melted and hot, stir in the flour and cook, stirring often, until it turns ivory color, about 5 minutes.
Stir in the heavy cream -- the mixture will seize up, but keep stirring -- then the milk. One cup should get you the consistency you want, which is a thin gravy. You might need more milk. Bring this to the steaming point or a very low simmer. Don't let it boil.
Mix in the dry mustard, parsley, and any of the optional ingredients you feel like using. Add salt and pepper to taste. White pepper is better here if you have it, but black pepper will do. Serve over your chosen protein, or potatoes.
Notes
It is important to not let this sauce boil.
Options and Tips
Lots of other fresh herbs will work here, like lovage, watercress, fresh oregano or marjoram, summer savory, tarragon or cutting celery.
You can add more dry mustard if you want, just stir in any extra 1/2 teaspoon at a time.
Don't use skim or lowfat dairy. The sauce will break.