Preheat the oven to 400°F/200°C/Gas 6 and prepare a lined baking sheet with parchment paper. Rub each beet with a bit of olive oil, pierce a few times with a fork, then individually wrap each beet in tin foil. Place the beets on the baking sheet and roast for for 1 to 1.5 hours or until easily pierced with a knife. Remove from the oven, allow to cool. They can now be easily peeled by rubbing. Grate or julienne the cooled beets and set aside.

Melt butter in a large french oven. When the butter begins to foam, add the prepared root vegetables (except for cabbage and potatoes) and saute until they have softened. Reduce the heat to low and stir in tomato paste.

Add the beef stock and bring to a boil (skim off the scum on the surface). Then add the cabbage (if using) and the potatoes. Reduce to a simmer and simmer for 10 minutes. Continue simmering gently, partially covered, for 40 minutes, adding more stock to thin the soup if needed.

Add the beets, cubed meat, and more salt if needed. Add lemon juice to taste. The exact amount of lemon juice will depend on your taste, but the goal is to strike a perfect balance between sweetness and acidity so your borscht is neither too sour, nor too sweet. Simmer for another 10 to 15 minutes, or until the beets are no longer dark-red and the garlic has mellowed out. Remove from heat and stir in the parsley or dill