1. Preheat your oven to 375°F. Butter a 9×13-inch baking dish generously to prevent sticking and add flavor.
2. In a medium saucepan over medium heat, melt the butter until it foams gently. Stir in the flour with a wooden spoon, cooking for about 1 minute to form a roux. This step is crucial—it thickens the sauce without lumps, just like Mama Lu always said, “Take your time, don’t rush the love.”
3. Slowly whisk in the milk, stirring constantly to avoid any lumps. Keep whisking until the mixture thickens and coats the back of a spoon, about 5-7 minutes. Season with salt, pepper, and garlic powder if using.
4. Remove the sauce from heat and stir in 1 ½ cups of the cheddar and all the Parmesan cheese until melted and smooth. This cheesy sauce is the heart of the dish, so taste and adjust seasoning as you go.
5. Arrange a layer of potato slices in the bottom of your prepared dish, overlapping slightly. Pour a ladle of the cheese sauce over the potatoes, spreading it evenly. Repeat layering potatoes and cheese sauce until all the potatoes are used, finishing with a layer of sauce on top.
6. Sprinkle the remaining ½ cup cheddar cheese evenly over the top. This golden crust is what gives the dish its signature look and texture.
7. Cover the dish tightly with foil and bake for 45 minutes. Then, remove the foil and bake uncovered for an additional 25-30 minutes, or until the top is bubbly and golden brown, and the potatoes are tender when pierced with a fork.
8. Let the scalloped potatoes rest for 10-15 minutes before serving. This helps the sauce thicken up a little and makes it easier to serve.

I remember the first time I made this dish on my own in Portland, far from the Blue Ridge Mountains. I followed Mama Lu’s whispered advice to “watch the potatoes, not the clock,” and sure enough, the kitchen soon filled with that familiar aroma that felt like home. It’s those little moments that make cooking this dish special.