Slice carrots lengthwise into planks. Trim fronds from fennel and save for another use. Slice fennel bulb thinly. Toss carrots and fennel with 1 tablespoon olive oil and spread on a rimmed baking sheet. Roast for 20-25 minutes.
Meanwhile, add 1 tablespoon olive oil to a stockpot or Dutch oven set over medium heat. Add onion and stir to coat with oil. Cook, stirring occasionally, until quite soft and starting to caramelize. Stir in ginger, coriander, salt, and pepper and let spices toast a moment.
Add roasted vegetables and broth to the pot. Bring everything to a boil, then reduce to a simmer for 10 minutes. Taste and adjust seasonings as needed, then transfer to a blender and puree until smooth.