Cook the elbow macaroni according to the package instructions until al dente. Drain and set aside.

In a large pot, melt the butter over medium heat. Add the flour and whisk continuously for 2 minutes.

Gradually whisk in the milk and half-and-half until smooth. Continue cooking, stirring constantly, until the mixture thickens, about 5 minutes.

Reduce the heat to low. Stir in the shredded cheddar and Gruyère cheeses until melted and smooth. Add garlic powder, onion powder, paprika, salt, and black pepper. Stir well. Taste the sauce and adjust the seasonings as needed.

Add the cooked macaroni and crab meat to the cheese sauce. Gently stir to combine.

Pour the macaroni and cheese mixture into a greased 9x13-inch baking dish.

In a small bowl, mix the panko breadcrumbs with the melted butter until evenly coated.

Sprinkle the breadcrumb mixture evenly over the top of the macaroni and cheese.

Bake in the preheated oven for 30-40 minutes, or until the top is golden brown and the edges are bubbly.

Let the mac and cheese cool for 5 minutes before serving.