Olive oil cooking spray
2 teaspoon olive oil
1 medium onion, halved lengthwise and thinly sliced
1/2 teaspoon sea salt, divided
Fresh ground black pepper, to taste
2 cloves garlic, finely chopped
3/4 teaspoon dried thyme
1 1/2 tablespoon whole-wheat flour
2 cups low-fat milk
3 oz low-fat Monterey Jack or white cheddar cheese, grated
2 1/2 lb russet potates, peeled and sliced as thin as possible (1/8 inch or less)
2 oz Parmigiano-Reggiano cheese, grated
2 tablespoon whole-wheat panko (Japanese bread crumbs)

2 teaspoon olive oil 1 medium onion, halved lengthwise and thinly sliced 1/2 teaspoon sea salt, divided 2 cloves garlic, finely chopped 3/4 teaspoon dried thyme 1 1/2 tablespoon whole-wheat flour 2 cup s low-fat milk 3 oz low-fat Monterey Jack or white cheddar cheese, grated 2 1/2 lb russet potates, peeled and sliced as thin as possible (1/8 inch or less) 2 oz Parmigiano-Reggiano cheese, grated 2 tablespoon whole-wheat panko (Japanese bread crumbs)

1. Preheat oven to 350. Coat a 2-qt baking dish with cooking spray.
2. Heat oil in a large skillet over medium-high heat. Add onion, 1/4 teaspoon salt and pepper. Cook, stirring frequently, until lightly browned, about 7 minutes. Reduce heat to low and add garlic, thyme and flour. Cook, stirring constantly, for 1 to 2 minutes or until onions are coated with flour. Add milk and increase heat to medium-high. When liquid begins to simmer, reduce heat to low and cook until mixture thickens slightly, about 4 minutes. Add three-quarters of Monterey Jack and remaining 1/4 teaspoon salt, and stir until melted, and 1 minute. Remove from heat.
3. Arrange half of potatoes in an even layer in prepared baking dish. Cover with half of onion mixture. Repeat with remaining potatoes and remaining onion mixture.
4. In a small bowl, combine remaining Monterey Jack, Parmigiano-Reggiano and panko; cover and refrigerate until ready to use.
5. Bake potatoes in center of oven for 70-85 minutes or until potatoes in center of dish feel tender when pierced with a fork. When finished baking, remove potatoes from oven and sprinkle evenly with cheese-panko mixture. Preheat broiler to high and return baking dish to oven and broil until cheese is melted, about 2 minutes. Let cool for 10-15 minutes before serving.