Heat the oven to 350°F and coat a 7x11-inch baking dish lightly with butter or nonstick spray. The prepared dish should have an even film of fat so the set cheese squares release more easily.

Whisk the eggs, evaporated milk, garlic powder, onion powder, and kosher salt in a medium bowl, then work in the flour until the mixture looks uniform. Keep whisking until no dry pockets or flour lumps remain before adding anything else.

Fold the grated cheddar, Monterey Jack, and drained green chiles into the smooth batter, then spread it in the prepared dish and arrange the sliced jalapeños over the top. Bake for 25 to 30 minutes, until the edges are lightly browned, the cheese smells rich and savory, and the center has only a small gentle jiggle.

Set the hot dish aside for 5 to 10 minutes before cutting it into squares. The brief rest lets the custard firm up, so the pieces stay together instead of slumping onto the serving plate.