Preheat the oven to 400°F (200°C).
Cut the beets, carrots, and onion into 1 1/2-inch chunks, halve the head of garlic, and place them on a baking sheet with the prunes and bay leaves (line it with parchment to avoid stains). Drizzle with olive oil and season with 1 tsp of salt.
*If my beets and carrots are organic, I don't even bother peeling them.
Roast the vegetables in the preheated oven for 45-55 minutes, or until, if tested with a fork, they are tender and caramelized (especially the head of garlic).
About 15 minutes before your timer for the roasting veggies goes off, in a large pot, bring the water or vegetable broth to a boil.
Quarter the half head of green cabbage, discarding the hard part of the center. Add the cabbage to the broth, stir well, and bring it to a simmer. Let it simmer for about 10 minutes, or until the cabbage looks translucent and thoroughly cooked.
When your veggies are done, take the tray out of the oven, pick out the garlic, squeeze it into the pot of simmering cabbage, and discard the peel. Transfer everything else from the baking sheet to the pot, including the bay leaves.
Cover the pot and let the borscht simmer for 10 minutes, or until the flavors have melded together. Skim the top to remove any foam.
Remove the bay leaves from the pot and use an immersion blender or a regular blender to puree the soup until smooth. If using a regular blender, be sure to allow the soup to cool slightly before blending to prevent burns.
Stir in the red wine vinegar and season the soup with the additional 1/2 tsp of salt, if needed. Be careful with the salt to not compromise the natural sweetness of the vegetables combined with the prunes. Taste and adjust as you go — I never had to use more than 2 tsp of salt.