Preheat oven to 375 degrees F and line a baking sheet with parchment paper.
Cut squash in half, scoop out the seeds, and place cut-side down on baking sheet.
Peel celery root and cut into slices. Place on baking sheet next to squash, and drizzle celery root with olive oil or avocado oil and a generous pinch of sea salt.
Bake for about 45 minutes, or until squash is soft when pierced with a fork. Remove from oven.
In a large pot over medium heat, add the ghee or oil and then the leeks. Saute until soft and browned, then transfer them to a high-powered blender.
Scoop out the flesh of the kabocha squash, and add it to the blender along with the roasted celery root, stock, rosemary, thyme, 1 teaspoon of sea salt, turmeric, and black pepper. Blend on high until very smooth and creamy.
Return soup to pot. Bring to a boil, then reduce to a simmer for about 15 minutes, stirring occasionally.
Taste and add the remaining ½ teaspoon (or more) of sea salt, if desired. If you’d like some acidity, add the lemon juice and zest.
Top with roasted pumpkin seeds and serve.
Feel free to add more seasonings and herbs if you'd like, whether it be fresh sage, parsley, chili powder, etc.