Step 1

Preheat oven to 400 degrees.  Spray 9×13 inch casserole with olive oil or nonstick cooking spray.

Step 2

In large skillet over medium low melt butter. Add minced garlic and saute for 1 minute;  stirring constantly. Slowly whisk in flour; cook for 3 to 4 minutes whisking constantly.  Whisk in onion powder, paprika, dried parsley, salt and freshly ground black pepper.  Slowly whisk in chicken broth and milk; alternating between the two.  Whisk until smooth; simmer for 5 minutes. Turn heat to low and slowly whisk in 1/2 cups sharp cheddar and 3/4 cup white cheddar.  Simmer while you layer the potatoes.

Step 3

Layer 1/2 of the potatoes and 1/2 of the onions in the casserole dish.  Pour 1/2 of the cheese sauce over the potatoes.  Layer the rest of the potatoes and onions and and pour the rest of the cheese sauce over. Top with the remaining reserved cheese. Cover with foil and bake for 30 minutes.  Uncover and bake for another 30 minutes or until it is nicely browned on the top and bubbly.