Preheat the oven to 400°F. Spray a 9x9-inch casserole dish with non-stick cooking spray and set aside.
Cook the pasta: Bring 8 cups of water to a boil in a large saucepan or stock pot. Add 1½ teaspoons of salt, then stir in 8 ounces (about 2 cups) of elbow macaroni. Cook for about 5 minutes, or until the noodles just start to soften. Drain and return the noodles to the pan.
Prepare the egg mixture: In a medium bowl, whisk together 2 large eggs, 6 ounces (about ¾ cup) of the evaporated milk, 1 teaspoon dry mustard dissolved in 1 teaspoon water, and 1 teaspoon hot sauce. Set aside.
Add butter and cheese: Place the pot with the drained pasta over medium-low heat. Stir in 4 tablespoons unsalted butter and let it melt completely.Once melted, slowly pour in the egg mixture, stirring constantly. Add 4 ounces (about 1 cup) of shredded sharp white cheddar cheese and stir until melted and creamy.
Finish the sauce: Gradually add the remaining 6 ounces (about ¾ cup) of evaporated milk and 6 ounces (about 1½ cups) of shredded sharp yellow cheddar cheese. Stir until smooth and creamy. Season with ½ teaspoon salt and ½ teaspoon black pepper,
Assemble the casserole: Pour the macaroni and cheese mixture into the prepared 9x9-inch baking dish. Sprinkle 4 ounces shredded sharp cheddar cheese evenly over the top.
Make the topping: In a small bowl, combine 3 tablespoons melted butter, ⅓ cup panko bread crumbs, and ⅓ cup regular bread crumbs. Sprinkle the mixture evenly over the top of the casserole.
Bake: Place the dish in the oven and bake for about 20-30 minutes, or until the bread crumbs are golden brown and the edges are bubbly.
Serve: Let cool slightly, then serve warm and enjoy!