Bring a large pot of salted water to a rolling boil. Add the elbow macaroni and cook until al dente, about 8 minutes. Drain and rinse under cool water.

In a medium saucepan over medium-low heat, melt butter. Stir in flour to create a roux, cooking for about 1 minute. Gradually whisk in milk until the sauce thickens.

Stir in shredded Monterey Jack cheese until melted and velvety.

Fold in cooked macaroni and drained diced green chiles into the cheese sauce. Mix until evenly coated. Adjust seasoning with salt and pepper.

Preheat your oven to 350°F (175°C). Grease a baking dish, pour in macaroni mixture, and sprinkle more cheese on top. Bake for 25–30 minutes.

Let cool for about 10 minutes before serving. Garnish with cilantro and jalapeño slices if desired.