Preheat oven to 350°F (175°C).
Cook elbow macaroni according to package instructions until al dente. Drain and set aside.
In a large saucepan, melt butter over medium heat.
Whisk in flour and cook for 1-2 minutes until slightly golden and bubbly.
Gradually whisk in whole milk, continuing to stir until sauce thickens, about 5-7 minutes.
Remove sauce from heat and stir in garlic powder, salt, black pepper, sharp cheddar, and Monterey Jack cheese until melted and smooth.
Add cooked macaroni to cheese sauce and mix until fully coated.
Pour mac and cheese mixture into a greased baking dish.
Sprinkle panko breadcrumbs evenly over the top.
Bake in preheated oven for 20-25 minutes, or until the top is golden brown and crispy.
Let cool for 5 minutes before serving.