- 3 tablespoons butter
- 1 small white or yellow onion, peeled and thinly sliced
- 4 large garlic cloves, minced
- 3 tablespoons all-purpose flour
- 1 cup chicken stock or vegetable stock
- 2 cups milk (I used 2% low-fat milk)
- 1 teaspoon Kosher salt
- 1/2 teaspoon black pepper
- 2 teaspoons fresh thyme leaves, divided
- 4 pounds Yukon Gold Potatoes, sliced into 1/8-inch rounds (and peeled beforehand, if desired)
- 1 1/2 cups freshly-grated sharp cheddar cheese, divided
- 1/2 cup freshly-grated Parmesan cheese
1. Preheat oven to 400°F.
2. Melt butter in a large saute pan over medium-high heat and add onion, and saute until soft and translucent, about 4 to 5 minutes then add garlic and saute until fragrant, about 1 to 2 more minutes. Next, stir in the flour until it is evenly combined and saute for 1 more minute. Once done, pour in the stock, and whisk until combined. Add in the milk, salt, pepper, and 1 teaspoon thyme, and whisk until combined, cooking until the sauce comes to a simmer (not a boil) and thickens, about 1 to 2 minutes more. Now, please remove from heat and set aside.
3. Meanwhile, using cooking spray grease a 9 x 13-inch baking dish then spread half of the sliced potatoes in an even layer on the bottom of the pan. Now, you should top evenly with half of the cream sauce, the sprinkle evenly with 1 cup of the shredded cheddar cheese, and all of the Parmesan cheese. Make sure you use the remaining sliced potatoes, the remaining half of the cream sauce, and the remaining 1/2 cup of cheddar cheese evenly to top with.
4. Using aluminum foil cover the pan and bake for 30 minutes. Then remove the foil and bake uncovered for 25-30 minutes, or until the sauce is bubbly and the potatoes are cooked through.
5. Finally, remove and sprinkle with the remaining 1 teaspoon thyme and Serve warm.