Preheat your oven to 350°F (175°C). Grease your 9x13 inch baking dish with a bit of butter to prevent sticking.
In a large skillet over medium heat, melt 2 tablespoons of butter. Add in your choice of ground beef, cooking until browned and crumbly. Drain any excess fat.
Sprinkle the flour over the cooked beef and stir well. Gradually pour in the evaporated milk while stirring continuously to avoid lumps. Cook until the mixture thickens slightly. Remove from heat and stir in 1 cup of mozzarella cheese and the minced spinach.
In the greased baking dish, spread half of the cooked white rice evenly across the bottom. Pour half of the beef mixture over the rice, followed by half of the tomato sauce. Repeat the layers with the remaining rice, beef mixture, and sauce.
Top the casserole with the remaining 1 cup of mozzarella cheese. Dot the top with additional butter if desired for a golden finish.
Cover the baking dish with aluminum foil and bake in the preheated oven for 25 minutes. Remove the foil and bake for an additional 10-15 minutes, or until the cheese is bubbly and golden brown.
Once out of the oven, let the casserole sit for about 10 minutes before serving. This will help the layers set for easier slicing. Serve warm and enjoy!
