Ingredients

• 0.25 cups butter
• 3 cloves garlic
• 0.25 cups all-purpose flour
• 4 cups whole milk
• 1 tablespoon Dijon mustard
• 2 easpoonss t
• 1 teaspoon salt
• 1 teaspoon ground black pepper
• 2 teaspoons lemon zest
• 2 tablespoons lemon juice
• 3 pounds russet potatoes
• 1 cup onion
• 1 cup grated Parmesan cheese
• chopped fresh chives , for garnish
• black pepper , for garnish

Instructions

1. 1 Gather all ingredients.
2. 2 Preheat the oven to 375 degrees F (190 degrees C). Grease a 9x13-inch baking dish.
3. 3 Melt butter in a medium saucepan over medium heat. Add garlic and cook 30 seconds. Stir in flour and cook, stirring constantly, for 1 minute. Gradually whisk in milk, mustard, Worcestershire sauce, 1/4 teaspoon salt, and 1/4 teaspoon pepper. Cook, whisking constantly, until thickened and bubbly, then continue to cook and whisk 2 minutes more. Whisk in lemon zest and lemon juice. Remove from heat.
4. 4 Line bottom of prepared dish with 1/3 of potato slices; sprinkle with 1/4 teaspoon each salt and pepper, followed by 1/3 of onion slices, 1/3 of Parmesan cheese, and top with 1/3 of sauce. Repeat layers once more. Finally top with remaining potatoes, salt, and pepper, followed by remaining onion slices, and sauce.
5. 5 Sprinkle with remaining Parmesan cheese.
6. 6 Bake, uncovered, until potatoes are tender and top is golden brown, 50 to 60 minutes. Let stand 15 to 20 minutes before serving.
7. 7 Garnish with chives and/or cracked black pepper.

Nutrition per serving