Pre-heat the oven to 400 degrees. You’ll need a 9x13 pan for baking the casserole. You do NOT need to grease the pan.
Heat a large skillet over medium high heat, and melt the butter. Add the onion, pepper, cauliflower, carrot, and corn with a big pinch of sea salt. Sauté the veggies and the corn until soft and sweet, about 7-10 minutes.
Add the ground beef, liver, and taco seasoning, break up the beef, and brown the beef and liver with the veggies.
Once the beef/liver is browned, add the baby spinach, tomato sauce, and salsa, and bring to a simmer for a couple minutes. Turn the heat off, and taste the filling for salt and pepper to your taste.
Spoon 1/3 of the taco filling into the bottom of your 9x13 pan. Layer 6 corn tortillas, and then scoop another 1/3 of the taco filling over the corn tortillas. Sprinkle 1/2 cup or so of the cheese, and then layer the other 6 corn tortillas on top. Spread out the last 1/3 of the taco filling, and top with a good 1 cup or so of cheese to your liking.
Bake the taco casserole, uncovered, at 400 degrees for 10 minutes. Then, place the casserole under the broiler and broil for 3-5 minutes, until the cheese is golden on top.