You can buy beets already cooked, or you can cook your own. I steamed mine in the oven. Here's how: Clean and cut the tops off of the beets and place them cut-side down in ½ inch of water in a small baking pan. Cover tightly with aluminum foil and bake at 425 degrees F for 35-45 mins, until fork tender (will vary depending on the size of your beets). Allow to cool slightly, then the peels should come off easily when pulled.
My favorite brand of tahini is Pepperwood Organics (you can find it on Amazon), but Soom is also good.