Prehaeat oven to 400 F.

Cut each garlic head cross wise in haf (4 halves).
Drizzel cut surfaces with olive oil, season with sprinkle of salt and pepper.
Put the heads back together, wrap each in aluminum foil and place on baking sheet.
BAke until garlic is tender when squeezed, about 35 minutes.
Cool completely.

Squeeze soft garlic out of skin into a small bowel.
Add butter, salt, pepper (1/2 teaspoon each).
Mash together with a rubber spatula until well combined.

Cover tightly and refrigerate until ready to use (can be made up to three days ahead).

Bring to room temperature before using.