Preheat oven to 400 degrees Fahrenheit. Lightly spray a casserole dish with nonstick cooking spray.

Melt together Breakstone’s Butter and onions in a large skillet over medium-high heat. Cook, stirring occasionally, until softened, about 10 minutes. At this point, you’ll want to add the wine and continue to cook another five minutes until the onions are deeply caramelized.

Add the garlic, then season with salt and pepper. Cook another two minutes, then remove from the heat.

In a medium-size saucepan, melt butter over medium heat. Mix in the flour and salt and stir constantly with a whisk for one minute. Stir in milk. Cook until mixture has thickened.

Stir in cheese all at once, and continue stirring until melted and smooth, about 30 to 60 seconds.

Pour one third of the milk mixture into the bottom of the baking dish. Layer in a third of the potatoes and half of the onions. Add another third of the milk mixture, then a third of the potatoes, and then the remaining onions. Add the remaining potatoes, then pour over the last of the remaining milk mixture. Try to pat the potatoes in an even layer.

Cover and bake one hour 45 minutes to two hours.

Remove the foil and top with more shredded cheese. Bake for another 20 minutes, until the cheese is golden and melty. Serve the dish warm, topped with fresh thyme, if desired.