Bring a large pot of salted water to a boil. Add the elbow macaroni and cook according to package instructions until just al dente (usually about 7-8 minutes). Drain and set aside.
In a medium saucepan, melt the butter over medium heat. Sprinkle in the flour and whisk continuously for about 1-2 minutes to cook out the raw flour taste, creating a smooth roux. Gradually add the whole milk, whisking constantly to avoid lumps. Bring the mixture to a gentle simmer and cook until it thickens, about 5 minutes.
Reduce the heat to low and stir in the shredded cheddar and Monterey Jack cheese until melted and smooth. Mix in the chili powder, garlic powder, onion powder, salt, and pepper. Taste and adjust seasoning as needed.
In the pot or a large mixing bowl, combine the cooked macaroni, cheese sauce, sweet corn, and chopped green onions. Stir gently to evenly incorporate all ingredients.
In a small bowl, mix the breadcrumbs with grated Parmesan cheese. If using, add the crumbled cooked turkey bacon for extra flavor and crunch.
Transfer the macaroni and cheese mixture to a greased baking dish. Sprinkle the breadcrumb topping evenly over the surface. Bake in a preheated 350°F (175°C) oven for 20-25 minutes, or until the topping is golden brown and crispy.
Allow the bake to cool slightly before serving. This Sweet Corn Elote Mac and Cheese Bake pairs beautifully with a fresh salad or steamed vegetables for a complete meal.
