Preheat oven to 400F. Place a pan over medium heat, then remove the casing from the chorizo. Add the chorizo to the skillet and fry, stirring to break it up, and cook for 7-10 minutes or until thoroughly cooked. Drain well and set aside.

Place a cast iron skillet over medium heat and add the butter. Let it melt, then remove the pan from the heat and place on top of a towel or oven mitt. Alternatively, melt butter in a microwave and pour into the skillet. Make sure the inside of the pan is evenly coated with butter.

Crack eggs open directly into the pan. Sprinkle with salt and pepper.

Sprinkle the chorizo evenly over the eggs.

Spread the cheese out over the top.

Bake for 15-20 minutes, or until cheese is bubbling. If you like runnier yolks in your eggs, bake them for less time.

Serve warm with the avocado, sour cream, and garnished with cilantro, if desired.