Cut the stems off the beets, wrap them in foil, and roast at 400ºF for about an hour, or until tender. Cool, peel and slice into chunks. Put everything but the olive oil into the bowl of a food processor and purée, pouring the olive oil in through the feed tube as it blends, until smooth.
Taste and adjust seasoning if needed. If it’s too thick, add more olive oil or water. Store in the fridge.