Preheat the oven to 350°F (175°C). Bring a medium pot of salted water to a boil. Add the elbow macaroni and cook until just shy of al dente, about 2 minutes less than the package instructions indicate. Drain the pasta and transfer it to a large mixing bowl. Immediately toss the hot macaroni with 2 tablespoons of unsalted butter until the butter is melted and the pasta is evenly coated. Set aside.

In a large saucepan over medium-high heat, melt 3 tablespoons of unsalted butter, making sure it does not brown. Add the flour and whisk to form a smooth paste, cooking and stirring until the raw flour smell disappears, about 1 minute. While whisking constantly, slowly pour in the milk in a thin, steady stream to maintain a smooth, homogeneous sauce. The mixture will thicken, then thin out as you add all the milk. Continue to heat, stirring, until the sauce reaches a simmer and thickens slightly.

Reduce the heat to medium-low. Gradually whisk in the shredded sharp cheddar cheese until the sauce is smooth and fully emulsified; be careful not to let the sauce reach a boil after the cheese is added. Whisk in the hot sauce, a pinch of kosher salt, dry mustard, and garlic powder until everything is fully combined. I like adding a dash of hot sauce for a little extra kick—feel free to adjust to your taste.

Scrape the finished cheese sauce (from Step 3) into the bowl with the buttered macaroni (from Step 1) and mix well until all the pasta is evenly coated. Let the mixture cool slightly, then stir in the grated Gruyère cheese. Transfer the mixture into a greased 9-by-13-inch baking dish and, using a spatula, smooth the surface into an even layer.

Add the panko crumbs to a small mixing bowl. Melt the remaining 3 tablespoons of unsalted butter, pour it over the panko, and mix until all the crumbs are evenly coated. Season lightly with kosher salt. I always check for even butter distribution to make sure the crust turns out perfectly golden and crunchy.

Scatter the buttery panko mixture (from Step 5) evenly over the entire surface of the macaroni and cheese (from Step 4). Place the baking dish on the top rack of the oven and bake until the topping is browned and the edges are bubbling, about 35 to 40 minutes. Ovens may vary, so check occasionally to prevent the top from burning.

Remove the baking dish from the oven and let the mac and cheese rest for about 15 minutes before serving. This allows the casserole to set, making it easier to slice and serve neatly. For leftovers, I find reheating in the oven maintains the crisp topping, but the microwave works in a pinch too!