Preheat your oven to 375°F (190°C) and grease a 9x13-inch baking dish with unsalted butter or cooking spray.

Peel and thinly slice the russet potatoes to 1/8 inch thick, placing them in cold water to prevent browning.

In a skillet, melt unsalted butter over medium heat, add minced garlic and sauté for about 1 minute.

Sprinkle all-purpose flour into the garlic and butter mixture, stirring well to create a roux; cook for 1-2 minutes.

Gradually whisk in milk and heavy cream into the roux, stirring until thickened (about 5-7 minutes).

Remove from heat and stir in shredded sharp cheddar and grated Parmesan until melted and smooth; season with salt, pepper, and paprika.

Layer half of the potato slices at the bottom of the baking dish, pour half of the cheese sauce, then repeat.

Cover with aluminum foil and bake for 40 minutes.

Remove foil and bake uncovered for an additional 20-25 minutes until top is golden brown and bubbly.

Test for doneness by inserting a knife into the center. If tender, let rest for 10-15 minutes before serving.

Garnish with chopped parsley before serving.