01 - Preheat the oven to 400°F. Line a baking tray with parchment paper.
02 - Spread the butternut squash cubes on the tray, drizzle with 1 tsp olive oil, season with salt and pepper, then roast for 25 minutes until tender and lightly browned.
03 - Meanwhile, boil salted water and cook macaroni according to package instructions until al dente. Drain and set aside.
04 - In a large saucepan, melt butter over medium heat. Add chopped onion and minced garlic, cooking until softened for 3 to 4 minutes.
05 - Stir in flour and cook for 1 minute. Gradually whisk in milk and cook, stirring constantly, until the sauce thickens, about 5 minutes.
06 - Add the roasted squash to the sauce and blend with an immersion blender until smooth.
07 - Stir in cheddar, Parmesan, nutmeg, mustard powder, salt, and black pepper. Remove from heat once cheese melts and the sauce becomes smooth.
08 - Mix the cheese sauce with the drained macaroni, then pour into a lightly greased baking dish.
09 - In a small bowl, toss panko breadcrumbs with 2 tsp olive oil and grated Parmesan. Sprinkle evenly over the pasta.
10 - Bake for 15 minutes until golden and bubbling. Let stand for 5 minutes before serving.