Cook the pasta: Boil ziti in salted water until just al dente (1–2 minutes shy of the package). Drain and reserve ½ cup pasta water.
Crisp the pancetta: In a large skillet over medium heat, cook pancetta until golden and crispy. Use a slotted spoon to transfer to a paper towel-lined plate. Leave a little rendered fat in the pan.
Make the pumpkin sauce: In the same skillet, add olive oil or butter if needed. Sauté garlic until fragrant, about 1 minute. Stir in pumpkin purée, milk, broth, nutmeg, chili flakes, and a pinch of salt and pepper. Simmer 3–5 minutes until warmed and slightly thickened. Stir in parmesan to melt. Add a splash of pasta water if it gets too thick.
Combine: Toss the cooked pasta with the sauce until coated. Fold in half the crispy pancetta and half the mozzarella (and ricotta, if using).
Bake: Transfer to a 9x13” baking dish. Top with remaining mozzarella, parmesan, and pancetta. Sprinkle chopped sage on top. Bake at 400°F for 20–25 minutes until bubbly and golden on top.
Serve: Let rest 5 minutes before scooping. Perfect with a simple arugula or brussels salad and a glass of wine.
Notes
Make-ahead: Assemble earlier in the day, refrigerate, and bake before serving (add 5–10 minutes bake time).