Roasted Butternut Squash Bake with Sweet Potato Pomodoro and Gruyere

1 jar Sweet Potato Pomodoro Sauce
1 pound Italian sausage, browned, drained and crumbled
1 onion, diced
2 cups cubed butternut squash*
4 cups sourdough bread, cut into 1-inch cubes
4 eggs, beaten
1 1/2 cups milk
6-ounces Gruyere cheese, shredded
1 tablespoon fresh sage, minced
1/2 teaspoon grated nutmeg
1 teaspoon salt
3 tablespoons butter, divided

*Available peeled and pre-cubed in most grocery stores.

Preheat oven to 350 degrees. Butter a 4-quart baking dish with 1 tablespoon butter. Boil squash for about 5 minutes. Whisk eggs, milk, cheese, sage and nutmeg. Saute the onion in 2 tablespoons butter. Pour half of the jar of sauce into the casserole dish. Evenly distribute the bread cubes, squash, sausage and onion over the sauce. Pour the egg mixture on top and allow to rest for about 10 minutes. Bake for 45 minutes, until golden and bubbly. Serve with remaining sauce on the side.
Serves 4-6