01 -
Lightly grease a 9-by-13-inch casserole dish with vegetable shortening and set aside. Preheat oven to 350°F (177°C).
02 -
In a large stockpot set over medium heat, combine unsalted butter, Velveeta cheese cubes, Rotel, cream of mushroom soup, and whole milk. Stir constantly until the cheese has fully melted and the mixture is smooth.
03 -
Add shredded chicken, cooked spaghetti, kosher salt, and black pepper to the cheese sauce. Toss mixture thoroughly to combine all ingredients evenly.
04 -
Pour the combined mixture evenly into the prepared casserole dish and smooth the top with a spoon. Sprinkle shredded cheddar cheese evenly over the surface, then top with panko bread crumbs.
05 -
Cover the dish with foil and bake in the preheated oven for 30 minutes, or until the cheese is bubbling and hot throughout.
06 -
Remove the foil and place casserole under the broiler for 3 to 5 minutes, monitoring closely, until the panko crumbs are golden brown. Be attentive as bread crumbs may brown quickly.
07 -
Remove casserole from oven and allow to rest for 5 minutes before serving. Garnish with crushed red pepper flakes according to taste.