In a medium bowl, add the 5 tablespoons of melted butter, panko, and mix well. Set aside.
In a small saucepan over medium-high heat, add 2 tablespoons butter. Stir and let it melt.
Add the flour to the skillet and cook for 2 to 3 minutes, whisking continuously and making sure there are no lumps.
Whisk in the milk, broth, Dijon, and cayenne. Whisk occasionally until it begins to thicken.
Remove from the heat and stir in 1/2 cup of Swiss and a 1/2 cup of Monterey Jack, salt and pepper, stir until completely melted.
Pour the sauce over the casserole.
Sprinkle the remaining cheese over the top, followed by the panko mix.
Bake until the top is browned and the casserole is bubbling about 25 to 30 minutes.