Heat butter and bacon grease in a large pot over medium heat. Add carrots and onion; cook and stir until carrots are soft and onion is translucent, 5 to 10 minutes. Season with salt and pepper. Stir in 1/2 of the thyme leaves and cook until fragrant, 10 to 15 seconds.
Add stock, sweet potato, ginger paste, and remaining thyme; bring to a boil, Reduce the heat and simmer until sweet potato is soft, 15 to 20 minutes. Stir in orange juice, brown sugar, pepper flakes, and cinnamon.
Purée soup with an immersion blender until smooth, adding more stock if necessary to reach desired consistency. Stir in half-and-half and serve.