Heat butter in saucepan over medium / high heat
Add squash, carrots, onion, garlic powder, mustard, and salt
Sauté 5 minutes, or until onion is translucent
Add coconut milk and bring to simmer
Allow to simmer for 10 minutes, or until vegetables are tender and coconut milk has reduced by 1/2 and is thick
Pour veggies and coconut milk into blender / food processor and puree until smooth
Add egg yolk to puree and blend well
Check seasonings and add more salt or pepper to taste
Serve over veggies or protein of choice