Preheat the oven to 450º. Place the tortillas directly on the oven rack to warm while the oven is preheating. This should take 5-10 minutes, but keep an eye on them.

In a medium bowl, combine 1 Tbsp of taco seasoning with 1 Tbsp of flour. Whisk in the tomato sauce, 1¾ cups of water, 2 Tbsp of oil, and 2 tsp of vinegar. Season with a bit of salt and pepper.

Heat 2 Tbsp of oil in a large skillet over medium heat. Add the ground beef and a pinch of salt. Cook until the meat is browned thoroughly and drain off the excess fat.

Add 4 cloves of finely chopped garlic (I use the garlic press for this) to the beef and 1 Tbsp of taco seasoning. Cook for about a minute. Stir in the black beans with their liquid, and the drained corn. Cook for about 2 minutes, until the liquid starts to reduce a bit.

Spread ½ cup of the taco sauce on the bottom of a large baking dish, about 2-3 quarts.

Place 4 tortillas on the bottom of the dish, on top of the sauce. Cover with half of the meat mixture. and 1/3 of the sauce. Repeat this, then pour the remaining sauce over the top of the tortillas, spreading it to make sure it covers the entire top.

Bake the casserole for 15-18 minutes. Then let it sit for at least 5 minutes before serving.

In a small bowl, thin out the sour cream by adding 1 tsp of water at a time and stirring. Season with salt and pepper to taste. Drizzle over the top of the casserole and serve!