Dice the onion into 1/2-inch pieces, mince the garlic cloves, chop the cabbage into 1-inch pieces, slice the carrots into thin rounds (or half-moons for faster cooking), and slice the celery ribs into 1/4-inch crescents. Having everything prepped and ready ensures smooth cooking and even cooking times across all vegetables.

In a large pot, combine the broth with the diced onion, minced garlic, sliced carrots, and celery crescents. Bring to a boil over high heat, which takes about 5-7 minutes. This initial boiling helps soften the harder vegetables and infuse the broth with their flavors. I find starting with the longer-cooking vegetables ensures everything finishes at the same time.

Once the broth is boiling, add the chopped cabbage, diced tomatoes (with their juice), salt, pepper, oregano, basil, and red pepper flakes. Stir well to combine everything evenly. The cabbage will reduce as it cooks, so don't worry if it seems like a lot at first.

Reduce the heat to medium-low and simmer uncovered for 20 minutes, stirring occasionally. The soup is ready when all vegetables are tender and the flavors have melded together. I like to taste and adjust seasonings at this point—a pinch more salt or a dash more pepper can really brighten the flavors. Serve hot and enjoy!