Preheat oven to 350°F and place a baking rack in the middle of the oven. Lightly grease a large casserole dish with cooking spray and set aside.
Prepare my Ground Beef Taco Filling recipe and leave it in the pan. Mix cornstarch with water until the cornstarch has dissolved, then add to the beef mixture. Stir constantly and cook for 2-3 minutes, until the mixture thickens. Remove from heat and set aside.
Add two tortillas to the prepared casserole dish. Cut tortillas as needed to completely cover the bottom. Add half of the refried beans and carefully spread them on top of the tortillas without moving the tortillas. Add half of the beef mixture and spread it evenly. Add half of the beans on top of the beef mixture. Top with 1.5 cups of shredded cheese. Repeat.
Top with another layer of tortillas, spread fresh salsa over the final layer of tortillas and sprinkle remaining cheese over the top.
Bake in the preheated oven for 40-50 minutes or until the cheese is golden brown and bubbly.
Remove from the oven and place on a cooling rack. Let cool for several minutes before slicing and serving. Garnish with freshly chopped cilantro and a dollop each of sour cream and guacamole.