Preheat oven to 350. Separate beets from their stems and greens. Wash the beets, leave skin on (the beet skins will fall off easily after roasting), and place in a pan with 2 tbs olive oil, cover and put in oven.
They will take, depending on size, 45-60 minutes to cook. They are done when a knife slides easily through them. While they are cooking, wash the leaves thoroughly, remove any big stems, and tear into 2-3 inch pieces. When the roasted beets are almost done, put the other 2 tbs olive oil, chopped onion and garlic in large sautee pan. Heat over med-med low, adding the greens and cooking till they wilt down and become tender. Season with salt and pepper. Serve the greens as is, and the roasted beets sliced with either red-wine vingegar, or a tab of butter and salt and pepper.