Step 1: Prepare the Potatoes
• Preheat your oven to 375°F (190°C).
• Peel and thinly slice the russet potatoes (about 1/8 inch thick). You can use a mandoline for even slices.

Step 2: Make the Cheese Sauce
• In a medium saucepan over medium heat, combine the heavy cream, whole milk, minced garlic, salt, black pepper, and cayenne pepper (if using). Heat until just simmering, then remove from heat.
• Stir in the shredded cheddar and Gruyère cheese until melted and smooth.

Step 3: Assemble the Dish
• In a greased 9×13 inch baking dish, layer half of the sliced potatoes. Pour half of the cheese sauce over the first layer.
• Add the remaining potatoes and top with the remaining cheese sauce. Drizzle the melted butter over the top.

Step 4: Bake
• Cover the baking dish with aluminum foil and bake in the preheated oven for 30 minutes.
• After 30 minutes, remove the foil and bake for an additional 20–30 minutes, or until the potatoes are tender and the top is golden brown and bubbly.

Step 5: Serve
• Once baked, remove from the oven and let cool for a few minutes. Garnish with chopped chives or parsley before serving.
• Serve warm as a side dish to your favorite main course.