Preheat your oven to 375°F (190°C). Grease a 9x13-inch baking dish and set aside.

Bring a large pot of salted water (1/2 tsp salt) to a boil. Cook the shell pasta according to package instructions until al dente. Drain and set aside.

In a medium saucepan, combine the butternut squash, half & half, and broth. Bring to a simmer over medium heat and cook until the squash is fork-tender, about 10-12 minutes.

Use an immersion blender (or transfer the mixture to a blender) to puree the squash until smooth and creamy. Set aside.

In a large pot, melt the butter over medium heat. Whisk in the flour and cook for 1-2 minutes, stirring constantly, to make a roux.

Gradually whisk in the butternut squash puree, ensuring there are no lumps. Stir in the Dijon mustard, garlic powder, smoked paprika (if using), 1/2 tsp salt, and 1/4 tsp black pepper.

Reduce the heat to low and slowly add the cheddar, mozzarella, and Parmesan cheeses, one handful at a time, stirring until fully melted and smooth. Taste and adjust seasoning with the remaining 1/4 tsp salt and 1/4 tsp black pepper, if needed.

Add the cooked pasta to the cheese sauce and stir until evenly coated. Transfer the mixture to the prepared baking dish.

In a small bowl, mix the panko breadcrumbs with melted butter. Sprinkle the breadcrumbs evenly over the top of the mac and cheese.

Bake in the preheated oven for 20-25 minutes, or until the top is golden brown and crispy.

Let cool for 5 minutes before serving. Enjoy!