In a large pot, heat olive oil. Add in onion and sauté until translucent, about 10 minutes.
Stir in garlic and ginger and cook until fragrant, about 3 minutes.
Add in carrots, red curry paste. Cook for one minute. Add in vegetable broth and lemongrass. Bring to a boil and simmer for 15-20 minutes, or until carrots soften.
Add in coconut milk and cook for another 10 minutes. Remove lemon grass. Season with salt and pepper.
Pour soup into a blender, half at a time and puree until smooth. Be sure to have an opening at the top of the blender to let out the steam (tip: remove the centerpiece of the blender lid and use a kitchen towel to loosely cover the opening. This will avoid splattering while still letting out the hot air).
Divide soup into 4 bowls and top with cilantro, sliced Thai chili pepper and red pepper flakes.