Preheat oven to 350℉ (175℃) and lightly butter a 9x13 pan casserole dish.
In a small saute pan, melt 2 tablespoons unsalted butter over medium-low heat. Once the butter is melted, add in ½ small yellow onion (minced) and 4.5 ounces canned mild chopped green chiles and saute for 5-6 minutes or until the onions are softened. Set mixture aside.
In a small bowl, whisk together ½ cup milk, ⅓ cup all-purpose flour, and 1 teaspoon baking powder until completely smooth and incorporated.
In a large mixing bowl whisk 10 large eggs with 1 teaspoon seasoned salt , 1 cup cottage cheese, and 1 cup Colby Jack cheese (shredded). Add in the sauteed chile mixture and flour mixture. Be sure to whisk until all is well incorporated.
Pour the egg mixture into the prepared casserole dish and bake for 40-45 minutes or until eggs puff up and are set.
Serve warm or at room temperature.
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Notes
Note on Cheese: Colby Jack, Monterey Jack, Swiss, or Cheddar Cheese all work well in this casserole, but keep in mind for the smoothest melt, grate the cheese from a block rather than using pre-grated cheese.Gluten-Free: Use a 1:1 gluten-free flour in place of the all-purpose flour. No Seasoned Salt? Use ¼ teaspoon garlic powder and ¾ teaspoon kosher salt.Halving Recipe: Cut the ingredients in half and bake in an 8x8 greased baking dish for 35-40 minutes. Make-Ahead Instructions:Prepare up to baking, cover with plastic wrap, and refrigerate it for up to 24 hours. Remove the unbaked casserole from the refrigerator and let it sit at room temperature for 30 minutes. After 30 minutes, remove the plastic wrap and bake as directed.Storage: Store leftover egg casserole in tightly covered baking dish (or transfer to airtight container) and store in the refrigerator for up to 5 days. Reheat on heat-safe plate in microwave as desired.