Toss together cubed squash, onions, garlic, oil, salt, and pepper. Pour on to baking sheet and spread into a single layer.
Once cooked, place in a food processor or blender and add the sage, half & half, and broth; pulse until smooth.
Remove foil, sprinkle with mozzarella cheese, and cook for an additional 15-20 minutes, or until cheese is melted and slightly golden.
Butternut Squash Sauce and sausage and kale mixture can be made a day ahead of time if refrigerated in an airtight container.