Prep time: 15 minutes | Cook time: 25 minutes | Total time: 45 minutes

Cook butternut squash in pot of boiling salted water for 8 to 10 minutes or just until tender; drain.
Melt butter in saucepan set over medium heat; whisk in flour and cook, whisking, for 1 minute. Whisk in milk; cook, whisking constantly, for about 5 minutes or until sauce is thickened and smooth. Add salt and pepper; remove from heat and stir in 1/2 cup Parmesan.
Preheat oven to 425°F. Grease rimmed 15- x 10-inch baking sheet. On lightly floured surface, roll out dough and stretch gently into 14- x 9-inch rectangle. Transfer to prepared pan; prick dough all over with fork. Bake for 12 to 15 minutes or until lightly browned.

Remove from oven; spread sauce over dough. Top with squash, remaining Parmesan, mozzarella and prosciutto. Sprinkle with sage.

Return to oven; bake on bottom rack for about 10 minutes or until crust is golden brown. Drizzle with reduced balsamic vinegar (if using).

Tip: Try replacing the mozzarella cheese with Gorgonzola for a richer taste that pairs well with the mild squash.