How to Make It
Preheat your oven to 400°F. Lightly coat a 2- to 3-quart baking dish with cooking spray.
Peel potatoes and place them in a bowl of cold water. Using a mandoline, slice potatoes into 1/8-1/4 inch rounds. Return slices to cold water until ready to use.
Stir together heavy cream, flour, thyme, garlic, 1/4 cup of the butter, and 1 teaspoon of the salt in a medium sauce pan over medium. Bring just to a boil; remove from heat.
Combine pepper and remaining 1 teaspoon salt in a small bowl. Combine chopped parsley and rosemary in a second small bowl.
Drain sliced potatoes, and pat dry. Place half of the potato slices evenly into prepared baking dish. Sprinkle with 1 tablespoon of the chopped herbs, half of the salt-pepper mixture, and half of the cheese. Repeat process with remaining half potato slices, 1 tablespoon of the herbs, remaining salt-pepper mixture and cheese. Pour cream mixture evenly over potatoes. Cover with aluminum foil, and bake in preheated oven 25 minutes.
Stir together panko, pecans, lemon zest, and remaining 1 tablespoon herbs and 1 tablespoon melted butter in a small bowl until combined well. Uncover potatoes; sprinkle evenly with panko mixture. Bake another 20 to 25 minutes, or until topping is golden and mixture is bubbling. Let stand 10 to 15 minutes before serving.