Preheat the oven to 350°F (175°C). Coat a 9×13-inch baking dish with butter to help prevent the egg mixture from sticking as it bakes.
Place the eggs in a large mixing bowl. Using an electric hand mixer or stand mixer, beat them until the mixture becomes pale, light, and frothy.
Add the all-purpose flour, baking powder, and salt to the whipped eggs. Continue mixing until the dry ingredients are fully incorporated and the batter is smooth without visible flour lumps.
Gently fold in the cottage cheese, shredded Mexican cheese blend, melted salted butter, and well-drained green chiles. Stir until all ingredients are evenly distributed throughout the egg mixture.
Transfer the mixture to the prepared baking dish and spread it evenly. Bake immediately, or cover the dish and refrigerate it overnight before baking.
For immediate baking, place the uncovered casserole in the preheated oven. Bake for 35–40 minutes, until the edges develop a golden-brown color and the center is completely set and firm.
Remove the finished egg bake from the oven and allow it to rest for approximately 5 minutes. Slice into portions and serve while warm.