Make the vegetable broth: Rinse and add the leftover stems from greens like dill, parsley, and cilantro to a pot of water. Let them simmer to create a fragrant broth, then remove the stems before adding the chopped vegetables.
Prepare the vegetables: While the broth is simmering, dice the potatoes into small cubes and place them in water to prevent darkening. Slice the leek into thin rings, chop the sweet bell pepper, celery, and garlic. Dice the carrots into small cubes, and separate the cauliflower into florets and smaller pieces.
Add potatoes and seasonings to the broth: Remove the stems from the broth and add the chopped potatoes, bay leaf, and peppercorns. Let them cook until tender.
Roast the veggies: In a preheated skillet, toss in the leek, bell pepper, and garlic. Roast for about 5 minutes, then sprinkle with coriander and add a chunk of butter for extra flavor.
Combine the vegetables into the soup: Add the roasted vegetables to the simmering broth along with the cauliflower and carrots. Stir well and season with salt, coriander, and black pepper to taste.
Simmer the soup: Cover the pot and let the soup simmer for another 5 minutes, allowing the flavors to meld together.
Serve and enjoy: Once the soup is done, serve it hot with a dollop of sour cream to balance the sweetness and enjoy the delicious, comforting flavors!