01 -
Preheat oven to 375°F (190°C) and lightly grease a 9x13 inch baking dish to prevent sticking.
02 -
Melt butter in a medium saucepan over medium heat. Add minced garlic and sauté just until fragrant, about 1 minute. Stir in flour and cook while stirring constantly for 2 minutes, forming a smooth, golden roux.
03 -
Reduce heat to medium-low. Gradually whisk in milk, pouring slowly to prevent lumps. Cook, whisking continuously, until the sauce thickens slightly, 3-5 minutes.
04 -
Add chicken bouillon powder or kosher salt, additional salt, and black pepper. Stir well and continue to cook until sauce is velvety and coats the back of a spoon. Remove from heat.
05 -
Arrange half of the sliced potatoes evenly in the prepared baking dish.
06 -
Pour half the cream sauce over the potatoes, spreading evenly. Sprinkle half of the mozzarella and half of the Parmesan cheese on top.
07 -
Layer remaining potatoes, pour over the rest of the sauce, then top with remaining mozzarella and Parmesan cheeses.
08 -
Cover dish tightly with aluminum foil and bake for 40 minutes to allow the potatoes to become tender.
09 -
Remove foil and continue baking for 30 minutes, or until the top is golden and sauce is bubbling. For a crispier top, broil on high for 1-2 minutes, watching closely to avoid burning.
10 -
Let the dish cool for a few minutes, then scatter chopped fresh chives over the top and serve warm.