Bring a large pot of lightly salted water to a boil. Add the elbow macaroni and cook until al dente. Drain and set aside.

In a medium saucepan over medium heat, melt the butter. Stir in the flour and whisk for 1-2 minutes until smooth. Slowly whisk in the milk until the mixture thickens, about 5-7 minutes.

Add the shredded cheddar and cream cheese, stirring until melted. Season with salt, garlic powder, onion powder, ground mustard, and black pepper.

Stir the cooked macaroni into the cheese sauce. Allow the mixture to cool for a few minutes, then mix in the beaten egg until well combined.

Preheat your oven to 400°F. Lightly coat a mini muffin tin with nonstick cooking spray. Spoon the mac and cheese mixture into each cup, filling nearly to the top.

Bake for 15 minutes or until the tops are lightly golden. Let the bites cool for a few minutes before gently removing them. Garnish with chopped green onions.