1. Preheat oven to 400°F (200°C) and line a baking sheet with parchment paper.

2. Toss cubed squash with olive oil, salt, and pepper; spread in a single layer and roast for 25–30 minutes, flipping halfway until golden and tender.

3. Cook pasta in a pot of salted boiling water according to package instructions; reserve 1/4 cup pasta water and drain.

4. In a large skillet over medium heat, melt butter and cook until it turns amber with nutty aroma, about 3–4 minutes.

5. Add sage leaves and garlic to brown butter, cook 30 seconds until fragrant and garlic is light golden, then remove from heat.

6. Add cooked pasta to skillet with butter, toss with reserved pasta water until sauce coats pasta evenly.

7. Fold in roasted squash cubes and grated Parmesan, season with salt and pepper to taste.

8. Divide pasta among plates and garnish with toasted walnuts, red pepper flakes, and crispy sage leaves if desired.

9. Serve immediately while warm and creamy.