Take a large rimmed baking sheet and line it with parchment paper or spray it with non-stick cooking spray. Add carrots to a baking sheet in a single layer (don’t let carrots touch) and drizzle them with olive oil. Using your fingers, spread the olive oil on the carrots so the exposed portion of each carrot is evenly coated with olive oil. Sprinkle salt, pepper, and garlic powder (optional) evenly across the carrots.
Roast for 20-25 minutes before turning the carrots over. Roast for an additional 10-15 minutes, or until the carrots have a nicely brown color and are fork tender. Remove from oven and cool.
When the carrots are cool enough to pick up, put them in a food processor (or high-powered blender). Add garlic, ginger, and 2 ½ cups of vegetable broth. If necessary, divide into even batches. Puree all ingredients until the mixture is smooth.
Next, pour carrot puree into a stock pot or Dutch oven. Add remaining broth, plus cumin, cinnamon, and allspice. Stir ingredients to combine and heat over medium heat.
Reduce heat to low. Add heavy cream gradually. To ensure the heavy cream doesn’t curdle, make sure the cream is at room temperature or slightly warmer before adding it to the pot.
Remove the soup from heat, and then season with salt and pepper to taste. Adjust other seasonings if desired. Serve immediately with a salad or your favorite crusty bread.