Preheat the oven to 425 degrees.

Prepare a large, rimmed baking sheet by lining it with aluminum foil. Spread the Brussels sprouts onto the sheet, and drizzle them with the olive oil and sprinkle with salt and pepper. Mix them with a spoon or your hands to coat them, and then, being sure to spread them out as much as possible, place the sheet in the oven and let the sprouts roast for about 15 minutes, stirring halfway through, until they are fork tender. When they are done, remove them from the oven, and set them aside.

While the sprouts roast, prepare the cavatappi in a large pot or Dutch oven, according to package instructions, and shred the cheeses. (You can combine the Gruyere and white cheddar while you do this, but keep the parmesan separate.)

When the pasta is done, drain it and set it aside.

Return the empty pot to the stove over medium heat and add five tablespoons of the butter. Once it is melted, whisk in the flour, garlic powder, ground mustard and cayenne. Continue to whisk it constantly until the mixture starts to foam a bit. As you whisk, slowly pour in the milk and continue whisking until everything is dissolved into the liquid.

Turn the heat up just a smidgeon and continue whisking regularly so the milk doesn’t scald, and let the mixture come up to a simmer (that moment just before it’s going to start boiling). Reduce the heat back down to low, still whisking regularly, and let the mixture reduce just a bit. It’s ready when it coats the back of a spoon. (This took me somewhere around 7 or 8 minutes.)

Remove the pot from the heat and stir in the Gruyere and white cheddar, mixing until it is completely melted. Add some salt and pepper, to taste. Once the sauce is flavored to your liking, stir in the pasta and sprouts, coating everything.

Dump everything onto the baking sheet you used for the sprouts, and spread it out evenly.

Turn the broiler in your oven to high.

Add the last tablespoon of butter to a microwave-safe bowl. Melt the butter in the microwave, and then stir in the parmesan and panko until everything is well combined. Sprinkle the panko mixture evenly over the top of the mac and cheese, and place the pan in the oven for a couple minutes, keeping a close eye on it, until the panko is lightly browned.

Serve immediately.