How to Make It
Preheat oven to 400°F. Toss together carrots, 1 tablespoon oil, 1 teaspoon salt, cumin seeds, and caraway seeds in a large bowl until evenly coated. Spread carrots in an even layer on a rimmed baking sheet lined with aluminum foil; roast in preheated oven until very tender and browned in spots, about 1 hour, stirring halfway through roasting.
Melt 1 tablespoon butter in a large saucepan over medium. Add onion, and cook, stirring often, until softened, about 6 minutes. Stir in roasted carrots and broth, and bring to a simmer over medium-high. Reduce heat to medium-low, and gently simmer until flavors meld, about 15 minutes. Transfer to a blender; add sour cream and remaining 1/4 teaspoon salt. Secure lid on blender, and remove center piece to allow steam to escape. Place a clean towel over opening. Process until soup has a smooth and silky consistency, about 1 minute and 30 seconds. Cover to keep warm.
Melt remaining 2 tablespoons butter and remaining 1 tablespoon oil in a large skillet over low. Add bread pieces, and cook, stirring occasionally, until bread is crisp on the outside and slightly chewy in center, 10 to 12 minutes. Transfer to a small bowl, and sprinkle with salt.
Divide soup among 4 warm shallow bowls. Top each bowl with 2 tablespoons bread and 2 tablespoons crumbled cheese. Sprinkle servings evenly with dill and chives.