Preheat the oven to 350 degrees F and prepare a 9x13 baking pan with a light coating of nonstick spray. Set aside.
In a small frying pan, melt 3 tablespoons butter over low heat. Add the panko or breadcrumbs and stir for about 3 minutes or until lightly toasted. Remove from heat and set aside.
In a small saucepan, melt the remaining 3 tablespoons of butter over medium heat. Add the 3 tablespoons of flour and whisk constantly for 3 minutes.
Slowly add the milk and cream, ½ cup at a time whisking constantly until smooth and bubbly. Simmer for a few minutes or until thickened. Remove from heat. Add the spices and cheese, stirring until melted and smooth.
In the prepared baking dish, combine the pasta and cheese sauce and stir until evenly coated. Gently fold in the crab mixture and top with the prepared breadcrumbs.
Bake for 25 minutes or until the dish is hot, bubbly and golden brown.
Notes
To store leftovers, transfer cooled casserole to an airtight container and refrigerate for 3-4 days.
Reheat in the microwave, adding a splash of milk or cream if it seems dry. Or, reheat in a small casserole dish in the oven for a crispy topping.