Preheat oven to 375 degrees. Slice half an inch off tops of garlic heads and place on baking sheet.
Drizzle olive oil over garlic and cover with tented foil. Roast in oven for 1 hour. Remove garlic from oven and let cool until able to handle.
Squeeze roasted garlic out of the skin into food processor or blender. Add butter, salt, Worcestershire and parsley, then blend all ingredients together.
Place mixture in middle of a large piece of plastic wrap. Form into a log and wrap tightly. Refrigerate 4-6 hours. Butter will keep for several weeks in refrigerator; slice off medallions as needed.