Preheat your oven to 375°F (190°C).
In a large pot, bring salted water to a boil. Add the diced potatoes and cook for about 10-12 minutes, or until fork-tender. Drain and set aside.
In a medium saucepan, melt the butter over medium heat. Add minced garlic and sauté until fragrant, about 1 minute.
Reduce the heat to low and add the heavy cream, stirring to combine. Gradually whisk in the cheddar and mozzarella cheeses until melted and smooth. Season with salt, pepper, and paprika (if using).
In a large baking dish, layer the cooked potatoes, and pour the creamy cheese sauce over the top, ensuring all the potatoes are well coated.
Use a spatula to gently mix the potatoes and cheese sauce together.
Cover the dish with aluminum foil and bake in the preheated oven for 30 minutes.
Remove the foil and bake for an additional 15 minutes, or until golden and bubbly.
Once cooked, remove from the oven and let it sit for a few minutes before serving. Garnish with chopped parsley if desired.