In a large stockpot, heat grapeseed oil over medium-high heat. Add the onion and cook until translucent, stirring continuously. Add the garlic and continue to cook until soft and fragrant, stirring for another couple of minutes.
Add the rutabaga and bone broth. Bring to a boil, then turn down to a simmer. Cook, covered, for 10 more minutes.
Add the broccoli, mushrooms, water, and salt. Return to a boil just for a moment. Reduce heat and simmer, covered, for another 10-15 minutes, until all of the vegetables are just soft.
Add the coconut milk to the pot and stir to combine.
Remove from heat and blend until creamy. You can use an immersion blender to do it right in the cooking pot, or you can use a countertop blender to puree in batches.