Peel butternut squash. Cut in half lengthwise and scoop out seeds. Cut flesh into cubes.

Melt butter and coconut oil in a soup pot over medium-high heat. Add onion and cook until translucent, about 3 minutes. Add squash, red peppers, red curry paste, ginger, and garlic. Mix thoroughly and cook for 5 to 7 minutes. Add extra butter if the pot dries out, to avoid burning onion or squash.

Pour coconut milk and skim milk into the pot; bring to a boil. Reduce heat and simmer soup, stirring often, until squash is soft, about 25 minutes.