Bring a large pot of salted water to a rolling boil. Add penne pasta and cook 8-10 minutes until al dente, then drain and set aside. Reserve 1 cup of pasta water for adjusting sauce consistency later.

While pasta cooks, melt butter with olive oil in a large skillet over medium heat. Add minced garlic and sauté 2-3 minutes until fragrant, stirring constantly to prevent browning and ensure even cooking.

Stir in the pumpkin puree and vegetable broth, whisking until completely smooth. Cook 3 minutes while stirring occasionally, allowing flavors to meld and the pumpkin to warm through evenly.

Pour in heavy cream and whole milk slowly while stirring constantly to prevent lumps from forming. Reduce heat to medium-low and simmer 4-5 minutes until the creamy silky pumpkin alfredo recipe reaches a gentle bubble without boiling rapidly.

Remove from heat and stir in grated Parmesan cheese until completely melted and incorporated. Add salt, black pepper, nutmeg, and red pepper flakes, tasting and adjusting seasonings to your preference.

Add cooked penne to the skillet and toss gently to coat every strand with the creamy sauce. If the sauce seems too thick, add pasta water one tablespoon at a time until reaching desired consistency.

Divide among four bowls and garnish generously with fresh chopped sage. Serve immediately while the pumpkin alfredo is hot and the flavors are most vibrant.