Step 1

Halve leeks lengthwise; rinse thoroughly, pat dry, and cut into 1/2-inch slices. In a large Dutch oven or heavy pot, heat oil over medium-high. Add onion, carrots, and celery; cook, stirring occasionally, until softened, about 5 minutes. Add leeks and garlic and cook, stirring, until leeks begin to soften, 2 minutes. Add potato, broth, and bay leaves and bring to a boil. Stir in cabbage and season generously with salt and pepper.

Step 2

Return soup to a boil, then reduce to a rapid simmer. Cover and cook until vegetables are tender, 15 to 20 minutes. Remove from heat; stir in vinegar and thyme. Season with salt and pepper.