Preheat oven to 425°. Toss carrots with 2 tablespoon of olive oil, 1 teaspoon of salt, pepper, and dried thyme. Place on a baking pan and roast for 20 minutes 6-8 inches from the top of the oven. Then switch to broiler and broil for 5 minutes turning carrots every 1-2 minutes.
Remove carrots from the oven. Place carrots in a food processor with 1 cup of chicken broth and blend until smooth.
In the dutch oven, add 2 tablespoon of olive oil and bring to medium heat. Saute onions for 8 minutes or until translucent. Then add ginger and garlic and saute for 2 more minutes. Pour in 4 cups of chicken broth and bring to a boil. Then add sprig of thyme and basil and simmer for 10 minutes.
Stir in roasted carrot puree and mix well using an immersion blender. Or stir with a spoon until well-combined. Bring back to a low simmer for 15 minutes. Then stir in heavy cream.
Serve with croutons and a squeeze of fresh lemon juice
Notes
Broiling the carrots will bring out the sweetness in the carrot. DON'T STEAM THEM. Unless you want bland soup. This is a necessary step to balance the flavor of the soup. Definitely roast the carrots. You should get a nice little char and bubbling on the carrots. This will caramelize the sugars in carrots and make them sweeter. I learned this from the first chef I ever worked for.
It is okay to just whisk the pureed carrot into the soup but this will leave onions, ginger, and garlic chunks in the soup which will affect the texture. The taste will be the same but if you're a texture person, you have to use the immersion blender to get the best texture.