Pre-heat a large dutch oven or soup pan over medium high heat. Add the butter and onions and cook until onions are soft (about 5-7 minutes). The onions and butter shouldn't brown.
Add the minced garlic and stir until fragrant (30 seconds - 1 minute).
Add the broth, carrots, 2 tablespoons of ginger, cumin and red pepper flakes (if using) and stir to combine. Cover and bring to a boil.
Reduce the heat and simmer until the carrots are tender when pierced (approx. 20-25 min). Remove from the heat.
Purée the soup with an immersion blender. If you don't have an immersion blender, use a blender working carefully in small batches. Transfer the soup into the blender and purée until completely smooth. The soup will be HOT so only fill the blender halfway and keep a hand on the top to avoid hot liquid spurting out.
Return to the pan and stir in the whipping cream. Taste and adjust seasonings (ginger, salt, pepper) as needed.
OPTIONAL: If the soup has cooled significantly during the smoothing process, turn the stove back on and stir over high heat until hot.
Serve immediately or refrigerate for up to 5 days.