Preheat the oven to 400°F. Grease a 9×13-inch baking dish with butter/spray and set aside.

Place sliced potatoes into a large bowl and drizzle with garlic flavored olive oil. Use your hands to rub oil into all potatoes. Let sit while you prepare the cream sauce.

In a medium-sized sauté pan, melt butter over medium heat. Whisk in flour until dissolved. Pour in milk and chicken stock, stirring until mixture simmers, about 2 minutes.

Sprinkle in half of the gruyère cheese and all of the parmigiano-reggiano cheese, stirring until cheese has melted. Season with salt, pepper, and paprika; mix until well combined. Remove from heat.

Layer the potatoes upright in the prepared baking dish. Pour cream sauce over the potatoes, spreading sauce between potato layers if necessary.

Sprinkle remaining 1 cup of gruyère cheese on top of the scalloped potatoes.

Cover the baking dish with aluminum foil and bake for 30 minutes. Remove foil and bake for another 30-35 minutes, or until top is golden brown and edges are crispy.

Let scalloped potatoes cool for at least 10 minutes.

Garnish with chives if desired. Serve warm.