Preheat oven to 400 degrees F.
Place carrots on a baking sheet and drizzle with 2 tbsp olive oil. Sprinkle with 1/2 tsp sea salt and rosemary. Roast for 30 minutes. Remove from oven and set aside.
Add the remaining 1 tbsp of olive oil to a large soup pot on medium-high heat and add onions. Saute for 5 minutes or until translucent.
Add in garlic and ginger and cook for 1 more minute.
Chop carrots into bite-sized pieces and add to soup along with the vegetable stock.
Stir in 1 tsp sea salt and ground pepper and bring the soup to a boil. Once boiling lower the heat to a simmer and let simmer for 30 minutes.
Turn off the stovetop and remove it from the heat. Allow soup to cool until manageable to blend.
Using an immersion blender or in batches with a regular blender, blend soup until smooth.
Stir in coconut milk if using.
Serve warm sprinkled with red pepper flakes if desired.
Store in the fridge for up to 1 week. Freezes well.