Preheat oven to 350 degrees and butter to a 2-qt baking dish. Scrub, dry, peel if desired, and slice potatoes thinly (about 1/8" thick) and set aside.

Place a small saucepan over medium heat and melt butter. Add flour and whisk until incorporated and allow the flour to cook for about 1 minute. Whisk in evaporated milk until completely smooth. Allow the sauce to come to a bubble, and then reduce heat to low. Allow the sauce to simmer for about 2 minutes, then whisk in the salt, pepper and grated cheese. Stir until the cheese is completely melted and the sauce is smooth. Remove from heat.

Shingle the potato slices into an even layer along the bottom of the buttered casserole dish using about ¼ of the slices. Season the potatoes lightly with salt, and then pour about ¼ of the sauce over the potatoes and spread to cover. Repeat with remaining potatoes, ending with the sauce on top. (Don’t forget to season each layer of potatoes lightly with salt.)

Cover with foil and bake for about 1 hour, then remove foil and continue baking for an additional 15–20 minutes or until the potatoes in the center of the dish are tender and the top is golden and bubbly. (You can test by piercing the center of the casserole with a paring knife. If you feel any crunch, they will need to cook longer.)

Remove from oven and allow the dish to cool for 10 minutes before serving. Enjoy!