Step 1

Preheat the oven to 375 degrees Fahrenheit and line a rimmed baking sheet with foil. In a large (stain-proof!) mixing bowl, toss the beets, potato, and cauliflower with the salt, pepper, and two tablespoons of the olive oil. Arrange the vegetables in a single layer on the baking sheet. Roast in the pre-heated oven until the beets and potatoes are knife-tender; about 35 to 45 minutes.

Step 2

Near the end of the roasting time, heat the remaining tablespoon of olive oil in a 3-quart or larger lidded pot set over medium heat. Add the onion and cook for 5 to 7 minutes, until it begins to turn translucent. Add the garlic and cook for another minute, until fragrant.

Step 3

Add the broth and roasted vegetables to the cooking pot. Allow the mixture to come to a boil; cover, reduce the heat to low, and simmer until all of the vegetables are tender enough to mash against the side of the pot with a wooden spoon (about fifteen minutes).

Step 4

Puree the mixture using an immersion or countertop blender. Stir in the balsamic vinegar, then taste the soup and add additional salt and pepper as desired. Serve with sour cream.