Whisk together the eggs and the milk in a large bowl. Heat up a pan over medium heat. When the pan is heated, run the butter along the pan until it is lightly coated. Pour in the egg mixture. Scramble the eggs with a wooden spoon until the eggs are completely cooked through (about 3 minutes). Remove the eggs into a clean bowl. If the chorizo is in a casing, open it up and crumble the chorizo into the already hot pan. Continue to break apart the chorizo into small bits, until the chorizo is cooked through (about 5 minutes). Remove from the pan. Stuff a burrito shell with 1/4 of the eggs, 1/4 of the chorizo, a few scoops of black beans, 2 tablespoons of the taco cheese, some diced avocado, and 1 tablespoon of salsa. Add in hot sauce if you desire. Roll it up and enjoy! For extra deliciousness, toast the folded burrito on a pan to make the outside nice and crispy.