Roast the Poblano Peppers: Preheat your oven’s broiler to high. Place the poblano peppers on a baking sheet and broil them for 6-8 minutes, turning occasionally until all sides are charred and blistered. Once roasted, transfer the peppers to a bowl and cover with plastic wrap or a lid. Allow the peppers to steam for approximately 10 minutes, then carefully remove the skins, scoop out the seeds, and chop them into small pieces.

Cook the Pasta: In a large pot, cook the pasta according to the package instructions until al dente. Drain and set aside.

Make the Cheese Sauce: In a large saucepan, melt the butter over medium heat. Add the flour and whisk continuously for 2-3 minutes to make a roux, ensuring it doesn't burn. Gradually pour in the heavy cream while whisking to combine. Let the mixture simmer for 3-5 minutes, stirring occasionally until it thickens. Add the mustard powder, mascarpone cheese, smoked gouda, aged white cheddar, and sharp cheddar. Stir until the cheeses are melted and the sauce is smooth. Stir in the roasted poblano peppers, Cajun seasoning, cayenne, smoked paprika, black pepper, and kosher salt. Continue stirring until everything is well incorporated.

Combine the Pasta and Sauce: Add the cooked pasta to the cheese sauce, stirring to ensure every piece is coated with the rich, creamy sauce.

Prepare the Panko Topping: In a small bowl, mix the panko bread crumbs with a drizzle of melted butter (optional) to give it a golden, crunchy texture when baked.

Bake the Mac and Cheese: Preheat your oven to 350°F (175°C). Pour the macaroni and cheese into a greased baking dish, and evenly distribute the panko breadcrumbs on top. Bake for 20-25 minutes, or until the top is golden brown and bubbling.

Serve: Remove from the oven and let the mac and cheese cool slightly before serving. Garnish with fresh herbs if desired.