Heat 1 tbsp olive oil in a large skillet over medium-high heat. Add ground beef and cook, breaking it apart with a spoon, until browned. Drain off excess fat. Add chopped onion to the skillet and cook until softened, about 5-7 minutes. Stir in minced garlic and cook for another minute until fragrant.

Stir in 1 tbsp chili powder, 1 tsp cumin, 1/2 tsp smoked paprika, 1/4 tsp cayenne pepper (if using), 1/2 tsp salt, and 1/4 tsp black pepper. Cook for 1 minute, stirring constantly, until spices are fragrant.

Pour in 1/2 cup beef broth, scraping up any browned bits from the bottom of the pan. Bring to a simmer and cook until most of the liquid has evaporated, about 5 minutes. Remove from heat and set aside.

In a medium saucepan, heat 2 tbsp olive oil over medium heat. Whisk in 2 tbsp all-purpose flour and cook for 1 minute, stirring constantly, to create a roux.

Add 2 tbsp chili powder, 1 tsp ground cumin, 1/2 tsp onion powder, 1/4 tsp garlic powder, 1/4 tsp dried oregano, and a pinch of cayenne (if using). Cook for 1 minute, stirring constantly, until fragrant.

Gradually whisk in 2 cups chicken or beef broth until smooth. Stir in 1 (8 oz) can tomato sauce, 1/2 tsp salt, and 1/4 tsp black pepper. Bring to a simmer, then reduce heat to low and cook for 10-15 minutes, stirring occasionally, until the sauce thickens to your desired consistency. (If using store-bought, simply warm it slightly).

Preheat oven to 375°F (190°C). Lightly grease a 9x13 inch baking dish.

Pour about 1/2 cup of enchilada sauce into the bottom of the prepared baking dish and spread evenly.

Lay 4-5 corn tortillas over the sauce, overlapping slightly to cover the bottom of the dish. Spoon half of the beef filling evenly over the tortillas. Sprinkle 1 cup of Monterey Jack cheese over the beef. Drizzle about 1/2 cup of enchilada sauce over the cheese layer.

Repeat the layers: place another 4-5 tortillas, followed by the remaining beef filling, the remaining 1 cup of Monterey Jack cheese, and another 1/2 cup of enchilada sauce.

Top with the last layer of 4-5 tortillas, then pour the remaining enchilada sauce over the top, ensuring all tortillas are covered. Sprinkle the 1/2 cup of shredded cheddar cheese evenly over the top.

Bake for 25-30 minutes, or until the casserole is bubbling around the edges and the cheese is melted and lightly golden. Remove from oven and let stand for 5-10 minutes before serving. Garnish with fresh cilantro, sour cream, green onions, or avocado, if desired.