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 thoroughly rub oil into all potatoes. Let sit to infuse while preparing the cream sauce.

In a medium-sized sauté pan, melt butter over medium heat. Once melted, whisk in flour and stir until dissolved. Pour in milk and chicken stock, and continue stirring. Let mixture come to a slight simmer, about 2 minutes.

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

Layer the potatoes, upright in a vertical row, into the prepared baking dish. Repeat until all potatoes are in the dish. Pour cream sauce over the tops, using fingers or a spoon to spread sauce between potato crevices if necessary.

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

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

Let scalloped potatoes cool for at least 10 minutes. Garnish with chives, if desired. Serve warm.