Bring a medium pot over medium heat filled with salted water.
Once the water starts boiling, add the potatoes and cook for 5-7 minutes until fork tender. Don’t overcook or they may break apart. Transfer to a chopping board to cool.
Once potatoes are cooled, thinly slice them with a mandoline or sharp knife. Transfer to a greased small casserole dish or two single-serving oven-safe dishes and reserve.
Preheat the oven to 350°F.
Make the bechamel sauce by bringing a small pot over medium heat, add the butter, garlic and onions and cook for 2 minutes, until softened. Add the flour, salt and pepper. Cook, stirring until bubbly.
Pour the milk slowly while whisking frequently. Cook for another 1 or 2 minutes and continue stirring to thicken the sauce, give a stir and pour over the potatoes.
Spread the cheese over the potatoes and bechamel sauce evenly in the casserole dish and bake for 10 to 15 minutes until the cheese is melted, browned, and bubbling.
Sprinkle fresh parsley and let it sit for 5 minutes before serving.
Notes
Turn this into a main dish by adding bacon, ham, or sausage. Vary the cheese to change up the flavor. Gouda and parmesan are great options.