If you are starting with a bunch of beets and the greens look fresh and tender, cut them off and save them for soups or stir-frying. Trim the stem and root end of each beet, wash thoroughly and pat dry with paper towels. Wrap one large or 3 small beets, with a drizzle of olive oil, in individual foil packets. You can add salt and pepper if desired. Place packets on a baking sheet and place in a 350-400 degree oven. Bake for about 45 minutes (larger beets can take longer), flipping packets over halfway through cooking time. Beets are done when you can press your finger into the side of the packet and the beet feels soft. You can also open a packet and use a knife to test the beets. After removing from oven, let them cool until they can be handled easily. Unwrap each packet and use your fingers to just slip the skin off each beet. (If you rub a little oil onto your hands, you will have fewer stains to wash off later.) Store roasted beets in the refrigerator for up to a week.