Butternut Squash Potato Gratin

Name: Butternut Squash Potato Gratin
Ingredients: 2 cups whipping cream combined with 1/4 cup water; 2 plump garlic cloves, minced; 3 large Yukon Gold (or other gold) potatoes, peeled and thinly sliced; 1 small butternut squash, peeled, seeded and thinly sliced (you want about even quantities of potato and squash); Salt and lots of freshly ground black pepper; 1/3 pound pancetta, chopped, fried crispy-chewy; 1 bunch green onions, thinly sliced; 2 cups grated Gruyere cheese; 5 tablespoons butter