In a large bowl, combine all ingredients for the "Cream-less Cream Sauce" except the sweet potato. Set aside.
Fill a large pot half-way full with water. Add the sweet potato. Cover and place over high heat. When it comes to a boil, remove the lid. Cook until fork tender, about 10 minutes.
Keep the water boiling. Remove the sweet potato with a slotted spoon, spider, or small sieve and place into "cream" mixture.
Using an immersion blender (or food processor/blender), puree the sweet potato into the mixture.
Gratin
To the pot of boiling water, add the butternut squash for 4 minutes. Then add the kale and cook for one minute. Drain vegetables. (At this point you can discard the boiling water.)
To assemble the gratin, start by greasing a large baking dish with ghee. Ladle a scoop of the cream sauce to thinly coat the bottom of the pan. Arrange slices of butternut squash in one layer. Scatter some of the kale and shallot mixture over the top. Season with salt and pepper. Ladle one scoop of cream sauce over the top.
Repeat until all squash is used, about 3-4 layers. Pour remaining cream sauce over the top. Sprinkle salt, pepper, and a dash of nutmeg.
Bake for 1 hour at 375 F. Allow it to cool slightly before serving.
Recipe by Laughter and Lemonade at https://www.laughterandlemonade.com/butternut-squash-gratin/