Preheat your oven to 400°F (200°C). Toss the cubed butternut squash with olive oil, salt, and pepper. Spread on a baking sheet and roast for 25-30 minutes until very tender.

While the squash roasts, cook the macaroni in a large pot of salted boiling water according to package directions until al dente. Drain and set aside.

In a blender or food processor, combine the roasted butternut squash, milk, garlic, mustard powder, nutmeg, salt, and pepper. Blend until completely smooth and velvety.

Return the large pot to medium heat and melt the butter. Pour in the blended squash mixture and bring to a gentle simmer.

Remove the pot from the heat and stir in the grated cheddar and gruyere cheeses until melted and smooth.

Fold the cooked macaroni into the cheese sauce until well coated.

Transfer the mixture to a lightly greased 9x13 baking dish. Sprinkle the panko breadcrumbs evenly over the top.

Bake for 10-15 minutes, or until the cheese is bubbly and the breadcrumbs are golden and crispy. Serve hot!