BOIL large pot of water. Add sliced potatoes to boiling water and cook for about 5 – 7 minutes or until potatoes are just tender when pierced with knife. Drain well.

PREHEAT oven to 375°F. Coat 9-by-13-inch or similar-sized shallow baking dish with cooking spray and set aside.

WHISK together water and yogurt in medium bowl until well combined.

MELT butter in medium saucepan over medium-low heat. Add flour and whisk until mixture is bubbling and just beginning to color, about 2 minutes. Add garlic, stirring until fragrant, then gradually whisk in yogurt/water mixture; increase heat to medium and cook, stirring for several minutes until sauce is simmering, smooth and thickened.

REMOVE from heat and stir in thyme, salt and pepper.

ARRANGE about one third of potatoes in even layer over bottom of baking dish. Top with one third of sauce followed by one third of cheese. Repeat with two more layers of potatoes, sauce and cheese.

COAT sheet of foil with cooking spray and cover dish tightly, coated-side-down.

BAKE for 30 minutes. Uncover dish and bake for about 20 minutes longer or until top is golden and potatoes are tender when pierced with knife. Let stand for about 10 minutes before serving.