Preheat your oven to 350°F and lightly grease a 9x13 inch baking dish or similar size. While the oven heats, wash and peel the potatoes, then slice them into thin, even rounds (about 1/8 inch thick). Uniform slicing ensures even cooking throughout the dish. Set the sliced potatoes aside in a bowl of cold water to prevent browning while you make the sauce.

Melt the butter in a medium saucepan over medium heat. Once melted, sprinkle the flour over the butter and stir continuously for about 1 minute to create a roux—this cooks out the raw flour taste and helps thicken the sauce. Slowly pour in the evaporated milk while whisking constantly to prevent lumps from forming. Increase heat to medium-high and bring the mixture to a gentle boil, then immediately reduce heat and simmer for 2 minutes, stirring occasionally.

Remove the sauce from heat and stir in the salt, garlic powder, onion powder, and black pepper until well combined. Add the shredded cheddar cheese and stir until completely melted and smooth. Taste the sauce and adjust seasonings if needed. I like to add a tiny pinch of extra salt at this stage since potatoes benefit from well-seasoned sauce for proper flavor development. Set the finished sauce aside.

Drain the potatoes thoroughly and pat them dry with a clean kitchen towel. Spread about 1/4 of the potato slices in an even layer on the bottom of the prepared baking dish. Pour about 1/4 of the cream sauce from Step 3 over the potatoes. Repeat this layering process three more times, alternating potatoes and sauce, and finish with a layer of sauce on top. The final sauce layer ensures the top layer of potatoes cooks evenly and gets creamy. I find patting the potatoes dry prevents excess water from diluting the sauce.

Cover the baking dish tightly with aluminum foil and place it in the preheated 350°F oven. Bake covered for 1 hour, which allows the potatoes to cook through and become tender while the foil traps steam. After 1 hour, carefully remove the foil and bake uncovered for an additional 15-20 minutes, until the top is golden brown and the sauce bubbles slightly at the edges. The uncovered baking time creates a light golden crust on top while keeping the interior creamy.

Remove the dish from the oven and let it rest for 10 minutes before serving. This resting period allows the sauce to set slightly, making the scalloped potatoes easier to scoop and serve while they remain hot and creamy. The residual heat continues to gently cook the top layer, ensuring all potatoes are perfectly tender throughout.