Preheat the oven to 350 degrees F. Lightly brush 2 tablespoons melted butter into 4 (1½ cup) ramekins or 1 (6 cups or so) baking dish.
In a large bowl, stir together the remaining 2 tablespoons butter, butternut squash, 4 egg yolks, cream, vanilla, cheese, sage and a pinch of salt + pepper.
In another large, clean bowl, whip the eggs whites until they are fluffy and have formed soft peaks. Stir about a third of the whites into the butternut mixture to lighten, then gently fold in the remaining whites, being careful not to deflate them too much.
Divide the soufflé mixture into the prepared ramekins or dish. Bake until golden and puffy, 30 to 35 minutes, and serve immediately with fresh sage or rosemary and Parmesan.