Melt butter in dutch oven and add onions or leeks and carrots. Cover and cook on low heat for 30 minutes until carrots and onions are soft.
Add potatoes and chicken bone broth. Bring to a boil and skim off any foam, then reduce to medium heat and add thyme sprigs and red pepper. Cover and cook about 15 minutes until potatoes soften.
Add zucchini and squash and cook another 5-10 minutes until soft.
Turn off heat, remove thyme sprigs, and puree soup with an immersion blender.
Add salt, black pepper, coriander, turmeric, and nutritional yeast to taste.
Ladle into bowls and add fresh cream, if desired.