Roast the Squash: Preheat oven to 400°F (200°C). Toss cubed butternut squash and garlic cloves with olive oil, salt, and pepper on a baking sheet. Roast for 25 minutes until caramelized and fork-tender. Squeeze roasted garlic from papery skins and transfer with squash into a blender. Add broth and nutmeg; blend until silky smooth.

Boil Pasta: Bring a large pot of salted water to a rolling boil. Cook cavatappi pasta until 1 minute shy of al dente. Drain and set aside.

Make Velvety Cheese Sauce: In a large Dutch oven or deep skillet, melt 3 tbsp butter over medium heat. Whisk in flour and cook for 1 minute until bubbly. Gradually whisk in warm milk and heavy cream. Simmer for 3 to 4 minutes until thickened. Stir in Dijon mustard, pureed roasted butternut squash, salt, and pepper.

Fold in Cheeses & Pasta: Turn heat to low. Stir in shredded sharp white cheddar and Gruyère until completely melted and glossy. Gently fold in cooked cavatappi pasta until every spiral is generously coated in the luscious golden sauce.

Crispy Panko Topping & Bake: In a small bowl, toss panko, melted butter, minced sage, and grated Parmesan. Scatter over the mac and cheese. Transfer to a 9x13-inch baking dish (or bake directly in oven-safe skillet). Bake at 375°F (190°C) for 15 minutes, then broil for 2 minutes until topping is deeply golden, sizzling, and crisp. Garnish with whole fried sage leaves and serve piping hot.