Preheat oven to 350°F. Butter a 8x8" or 7x10" pan. Then line half of the potatoes on the bottom of the pan.
Melt the butter in a small sauce pan over medium-heat. Add in the garlic and cook for 1-2 minutes. Whisk in flour, salt and pepper. Let cook another minute.
Turn heat to medium-low. Slowly whisk in the milk and whisk until smooth. Bring to a light simmer to allow to thicken. Then stir in 3/4 cup cheese until melted and remove from heat.
Pour half of the sauce over the potatoes. Then sprinkle about 1/2 cup cheese over top. Line the remaining potatoes over top. Then add the remaining sauce and cheese over top.
Bake uncovered for 50-60 minutes, or until potatoes are fork tender an the top is golden brown.
If you like your potatoes with onions, add 1/2 cup chopped onions when cooking the butter. Then cook 2-3 minutes.
You can also turn this into a meal by adding leftover chopped ham to the middle layer.
Add a little crunch by adding 4 pieces cooked and crumbled bacon to the top.
To make-ahead:If making in advance, cut the baking time in half. Cover with foil and bake for about 30 minutes. Remove from oven and let cool. Once cooled, refrigerate overnight. When ready to serve the next day, remove from fridge and let sit at room temp for 30 minutes. Then bake uncovered for about 20 to 30 minutes, until the sauce has thickened and the cheese is golden and bubbly.