Cheesy Scalloped Potatoes

INGREDIENTS

1 1/4 lbs red potatoes, washed, but not peeled
1 1/4 lbs Yukon gold potatoes, washed, but not peeled
1 onion, sliced thinly
3 Tbsp butter
3 Tbsp all purpose flour
2 cloves garlic, minced
1 tsp dry mustard
1/4 tsp dried thyme
1/4 tsp paprika
salt and pepper, to taste
2 cups whole milk
1 cup cheddar cheese shredded
1/2 cup gruyere cheese shredded
1/4 cup Parmesan cheese grated
fresh chives, for garnish
fresh parsley, for garnish
additional 1/4 cup cheddar cheese, shredded
additional 1/4 cup gruyere cheese, shredded
additional 2 Tbsp Parmesan cheese, grated


INSTRUCTIONS

• Preheat oven to 400 degrees F.  Butter a 2 quart casserole dish and set aside.  
• Slice potatoes in 1/8" thin slices (I use this mandoline slicer), and set aside.  
• Add butter to medium saucepan, and heat over MED heat.  When butter is melted, add garlic and saute for 1 minute, until fragrant.  Add flour, whisk, and cook 1 minute.  Slowly add milk, whisking continuously, until no lumps remain.  Whisk over MED heat until mixture is thick and coats the back of a spoon.
• Turn off heat, add cheeses, dry mustard, thyme, paprika, salt and pepper, and stir until smooth.
• Layer half the potatoes and onion slices in prepared casserole dish, pour approximately half of the cheese sauce over potatoes and let sit for a minute.  Repeat with remaining potatoes, onions, and cheese sauce.
• Sprinkle top of potatoes with gruyere, cheddar and Parmesan.  Spray aluminum foil with cooking spray, then cover the casserole dish (sprayed side down).  Place casserole on a baking sheet and bake for 60 minutes.
• Remove foil and bake uncovered an additional 25-30 minutes.  Potatoes should be tender and cheese melted.  Broil on HIGH for a minute or two for extra browning and crispiness.
• Sprinkle top with chives and parsley and serve.

Source : https://www.thechunkychef.com/garlic-parmesan-cheesy-scalloped-potatoes/