Preheat the oven to 450°F. Line a large rimmed baking sheet with parchment paper or a silicone baking mat.

Spread the carrots on the baking sheet in a single layer, leaving a little space between the pieces. Drizzle with the olive oil and toss until every piece is evenly coated. Sprinkle with salt, pepper, and garlic powder (if using).

Roast for 20 to 25 minutes, then flip the carrots and roast for another 10 to 15 minutes, until browned in spots and fork-tender. Let cool for about 10 minutes.

Transfer the roasted carrots to a blender or food processor. Add the garlic, ginger, and 2 ½ cups of the vegetable broth. Blend until completely smooth, working in batches if needed and filling the blender no more than halfway.

Pour the carrot puree into a large pot or Dutch oven. Stir in the remaining 3 ½ cups of broth, the cumin, cinnamon, allspice, and cardamom (if using). Heat over medium heat, stirring occasionally, until steaming, about 5 minutes.

Reduce the heat to low. Slowly stir in the room-temperature heavy cream and heat through for 2 to 3 minutes without letting the soup boil.

Remove from the heat and season with salt and pepper to taste, adjusting the spices if desired. Serve hot with crusty bread, a salad, or a grilled cheese sandwich.