1. Place potatoes in a large bowl and set aside. Melt 1 tablespoon butter in a large nonstick skillet over medium heat. Add onion and garlic and cook, stirring occasionally, until softened, 3 to 5 minutes. Transfer to bowl with potatoes, add 1 teaspoon salt and 1/2 teaspoon pepper, and toss well to combine.
2. In a small bowl, whisk cream, flour, nutmeg, 1/2 teaspoon salt, and 1/4 teaspoon pepper. Generously grease a 4- to 6-quart slow cooker, then arrange about one-fifth of potatoes over bottom, overlapping slices slightly. Top with 1/3 cup Gruyere, followed by 1/3 cup cream mixture.
3. Repeat process four more times, finishing with remaining Gruyere and cream mixture (about 2/3 cup each). Cover and cook on high until potatoes are fully tender, about 5 hours.
4. Meanwhile, melt remaining 2 tablespoons butter in a medium skillet over medium heat. Add panko and cook, stirring frequently, until golden brown, about 4 minutes. Transfer to a small bowl and let cool completely, then stir in Parmesan and parsley and set aside.
5. When potatoes are finished, turn off slow cooker, uncover, and let sit 20 to 30 minutes to allow sauce to thicken. Sprinkle panko mixture evenly over top and serve.
Source: Hannaford fresh Magazine, October - November 2021