01 -
Preheat oven to 400°F (200°C) and lightly grease a 9×13-inch baking dish with cooking spray.
02 -
In a medium saucepan, melt butter over medium heat. Add minced garlic and sauté until fragrant, about 30 seconds. Whisk in flour and cook for 2 minutes, stirring constantly to form a smooth roux.
03 -
Reduce heat to medium-low. Gradually whisk in milk, about 1/4 cup at a time, ensuring a lump-free sauce. Bring to a gentle boil and cook until slightly thickened. Stir in chicken bouillon powder, salt to taste, and black pepper. Remove from heat and set aside.
04 -
Arrange half of the sliced potatoes in an even layer in the baking dish. Pour half of the cream sauce over them, then sprinkle with half of the mozzarella and half of the Parmesan cheese. Repeat the layering with remaining potatoes, sauce, and cheeses.
05 -
Cover the dish tightly with foil and bake for 40 minutes, or until potatoes are just tender.
06 -
Remove foil and bake for another 30 minutes until the top is golden and bubbly. For extra crispness, broil for 2 to 3 minutes watching closely. Garnish with fresh chives and serve warm.