You can roast your own beetroot if you like (though it will add a lot of time to the recipe). Wrap two large beetroot in aluminium foil, then pop them into the oven at 200C/400F for about 50 minutes. Check them near the end - you should easily be able to pierce them right through with a knife. If you can, they're ready to use. Once roasted and cool enough to handle, you should be able to remove the skin with your hands easily. If you can't, you likely need to cook them a little longer, so pop them back into the oven.