Microwave potato slices and 1 cup water in a shallow glass dish covered with plastic wrap at HIGH 10 minutes or until tender, stirring once after 5 minutes.
Drain and set aside.
Melt 2 tablespoons butter in a large saucepan over medium-high heat; add onion, and sauté 5 minutes or until tender.
Add potato slices, and toss gently; remove mixture from saucepan.
Melt remaining 2 tablespoons butter in saucepan over medium heat.
Gradually whisk in milk and gravy mix; whisk until smooth.
Add shredded cheese, whisking until cheese is melted.
Remove from heat, and stir in potato mixture.
Spoon into a lightly greased 2½-quart or 9-inch square baking dish.
Combine breadcrumbs and dried parsley flakes; sprinkle over potato mixture.
Bake at 400° for 25 to 30 minutes or until bubbly.
Notes / Tips / Wine Advice:
For testing purposes only, we used McCormick Original Country Gravy Mix.