Cheesy Scalloped Potaoes

I started by preheating the oven to 375 degrees (F). To make the sauce, I melted the butter in a medium saucepan over medium heat, then the diced onion was cooked in the melted butter until soft. Next, I stirred the flour thoroughly into the onions and added the milk and garlic using a garlic press. The sauce was stirred over medium/high heat until it began to bubble and thicken. I removed it from the heat and stirred in 2 cups of the grated cheese. The sauce was set aside. Next, I sprayed a deep 9x9 ceramic casserole dish with some cooking spray. A single layer of potato slices was layered in the bottom of the dish, followed by a sprinkling of snipped chives. Another layer of potato came next, followed by more chives. I continued like this until the potatoes were used up. The sauce was then poured over the potatoes and the whole thing was given a good shimmy shake on the counter top to get the sauce to ooze down into all the nooks and crannies. The top was sprinkled with the remaining 1/4 cup of cheese and another sprinkling of chives. I then placed the casserole dish on a baking sheet in case it bubbled over (it didn't) and baked it for 60 minutes until brown and bubbly.