Irish Cheddar Potatoes Au Gratin

Slice the potatoes and onions in a consistent size. ⅛ - ¼"
Cutting the potatoes on a mandoline will give consistent size to bake evenly.
Place the sliced potatoes in a bowl of water to keep from browning.
Slice the onion in half and cut in to consistent half rings about ⅛ - ¼"
Reserve for use.
Grate the Cheddar Cheeses and reserve aside.
Grease the baking dish with 1 tbsp of butter.

Heat a saucepan over medium heat and melt the two tablespoons of butter.
Add the flour and stir to combine to make the roux.
Stirring, cook for 1-2 minutes to cook the roux.
Whisk in the half & half and cream mixture. Adding slowly as you whisk, breaking apart and incorporating the roux.
Continue until all of the liquid and roux have incorporated.
Add the salt, black pepper, dry thyme and granulated garlic.
Bring the mixture to a medium simmer.
In small increments incorporate half of the grated cheese, whisk to combine as it melts. Reserve the remaining cheese for Au Gratin assembly.
Reserve until assembling. Use while the sauce is hot, it will be easier to assemble the dish.

Preheat the oven to 375°
In the greased baking pan begin layering the potatoes. Cover the bottom with a layer then top with a second layer of potatoes.
Season this layer of potatoes with some salt and pepper. A light amount is fine.
The potatoes are not seasoned so adding some S&P gives some additional flavor to the baked potatoes.
Second layer, add some of the sliced onions on top of the potatoes.
Add some of the reserved grated cheese to cover the onions.
Add some of the Au Gratin Cheese Sauce to cover the cheese.
You don't have to completely cover, as the dish bakes the sauce will incorporate with the other layers of sauce.
Repeat the process until the pan is full and ingredients have been used.
To finish the last layer of potatoes with onions, sauce and top with cheese.
Cover tightly with foil. You are ready to bake.
The potatoes can be made ahead and refrigerated. If choose to refrigerate, the bake time will be extended, possibly by 30 minutes.

Place the baking dish on a sheet pan.
This will catch any overflow of the ingredients as it bakes.
Bake for 1 hour 30 minutes. Check to see if the potatoes are knife tender.
Bake longer if necessary.
Remove the foil and bake for another 20 minutes until the top is browned.
Alternatively, brown the top of the Au Gratin under a broiler, If the potatoes are cooked this is a quick way to brown the top.
Be sure to keep an eye on it so it doesn't burn.
Once the potatoes are knife tender and the top is browned, remove from the oven. Serve immediately.
Enjoy!