Mix the butter and beet juice and simmer in a sauce pan on low to medium heat. It will start to thicken and reduce over the next 15-20 minutes. Stir it often and don't let it bubble or get too hot. It will thicken even more once it begins to cool, but keep it warm for drizzling.
Set the oven to 450. Get a large oiled cookie sheet and place the chopped potatoes on it, sprinkle salt and pepper over them, and put back in the oven. Stir it around so that each side browns.
After 10-15 minutes, add the asparagus to the pan and place back in the oven. Everything should be ready 15 minutes after that. Keep an eye to make sure nothing gets burned.
Pour the beet butter on an empty plate and place the vegetables on top, or mix them all together (see pictures).