Cut beef tenderloin into 3/4" slices. Heat 1 Tbsp butter in skillet over medium-high heat. Saute beef in margarine over medium high heat until browned, turning once.
Cook and stir 1 Tbsp butter, the cocoa, salt, garlic, and rosemary in the same skillet until bubbly. Gradually stir in the wine. Heat to boiling; boil and stir 1 minute.
To Freeze: Freeze beef and sauce together in a freezer safe container.
To Reheat: Reheat from frozen in a saucepan until sauce is hot and bubbly and meat is desired doneness.