01 - Set oven temperature to 375°F (190°C).
02 - Slice off the pumpkin's top to create a lid. Scoop out seeds and fibers. Season interior with a pinch of salt and pepper. Arrange pumpkin on a parchment-lined baking sheet.
03 - Place prepared pumpkin (lid aside) in oven and bake for 25 minutes until slightly softened while retaining shape.
04 - Boil a large pot of salted water. Add macaroni and cook to just al dente, about 1 to 2 minutes less than package timing. Drain well and set aside.
05 - Heat a medium saucepan over medium, melt 2 tablespoons butter. Add flour and whisk for 1 minute. Slowly incorporate milk and cream, whisking continuously until thickened, around 3 to 4 minutes.
06 - Lower to gentle heat. Add cheddar, Gruyère, and Parmesan cheeses, stirring until fully melted and smooth. Season with salt, pepper, nutmeg, and Dijon mustard. Remove from heat.
07 - Mix the drained macaroni thoroughly into the cheese sauce.
08 - Transfer the prepared macaroni and cheese into the blind-baked pumpkin, leaving enough space at the top for bubbling.
09 - Blend panko breadcrumbs with melted butter, Parmesan, and parsley. Evenly distribute mixture over the macaroni and cheese.
10 - Bake pumpkin, uncovered, at 375°F (190°C) for 40 to 45 minutes, or until filling is bubbling and pumpkin flesh is tender when tested with a knife. For a decorative lid, bake pumpkin lid alongside during the last 15 minutes.
11 - Allow dish to cool for 10 minutes before serving, making sure to scoop both cheesy pasta and tender pumpkin flesh into each portion.