Scalloped Potatoes

Prep the Potatoes:
Peel the potatoes and slice them into thin rings (about 1/8 inch thick) using a knife or mandoline. Set the slices in a bowl of cold water to prevent browning until ready to use.
Make the Cheese Sauce:
In a large pan over medium heat, melt the butter. Add the diced onion and sauté until translucent, about 3-4 minutes.
Stir in the garlic and thyme, cooking until fragrant, about 30 seconds. Add the flour and stir well, cooking for 1-2 minutes to remove the raw flour taste.

Slowly whisk in the chicken stock, ensuring there are no lumps. Gradually add the milk while whisking constantly until the mixture is smooth and thickened.

Stir in the Parmesan cheese, followed by the shredded cheese blend, a little at a time, until melted and smooth. Taste and adjust seasoning with salt and black pepper.

Assemble the Dish:
Preheat your oven to 350°F (175°C). Grease a 9×13-inch casserole dish.
Spread a thin layer of cheese sauce on the bottom of the dish. Add a layer of sliced potatoes, followed by a layer of thinly sliced onion, and spoon more cheese 

sauce on top. Repeat this layering process until all the potatoes and sauce are used, finishing with a layer of cheese sauce on top.

Bake Covered:
Cover the casserole dish with foil and bake for 30 minutes.
Fry the Crispy Onions:
While the potatoes bake, prepare the crispy onions:
Toss the thinly sliced red onions with a little milk then in the all-purpose flour, ensuring they are evenly coated.
Heat about 1 inch of vegetable oil in a frying pan over medium heat. Test the oil with a small piece of onion—it should sizzle immediately.
Fry the onions in batches, making sure not to overcrowd the pan. Cook for about 2-3 minutes per batch, or until golden brown and crispy.
Remove the onions with a slotted spoon and place them on a paper towel-lined plate. While still hot, season generously with salt.
Finish Baking:
After 30 minutes, remove the foil from the casserole dish and sprinkle additional shredded cheese on top. Return the dish to the oven and bake uncovered for another 30 minutes, or until the potatoes are tender and the top is golden and bubbly.
Garnish and Serve:
Once the potatoes are done, top with the crispy fried onions and garnish with chopped parsley. 
Serve warm and enjoy!