Best Scalloped Potatoes

Preheat your oven to 375°F (190°C). Grease a 9×13-inch baking dish.
In a saucepan, melt butter over medium heat. Add diced onions and sauté until softened, about 3 minutes. Add minced garlic and cook for another minute.
Stir in the flour and cook for 1-2 minutes, forming a roux.
Gradually whisk in the milk and heavy cream, stirring constantly until the mixture thickens.
Remove from heat and stir in shredded cheddar cheese and Parmesan cheese until melted and smooth. Season with salt and pepper.
Layer the sliced potatoes in the prepared baking dish. Pour the cheese sauce over the potatoes, making sure they are fully covered.
Bake uncovered for 45-50 minutes, or until the potatoes are tender and golden brown on top.
Garnish with fresh parsley and serve warm.
Serving and Storage Tips: