Melt butter in a large pot over medium heat. Add onion and garlic, sauté for 3-4 minutes until fragrant.
Pour in broth. Add potatoes and carrots. Bring to a boil, then simmer for 15-20 minutes until tender.
Stir in pickles and pickle juice. Simmer for 5-10 minutes. Adjust juice for desired tanginess.
Whisk sour cream and flour in a small bowl. Temper with hot soup to avoid curdling.
Stir tempered sour cream mixture into soup. Simmer for 5 minutes to thicken. Season with salt and pepper.
Ladle into bowls, garnish with fresh dill, and serve immediately.
