Pre-heat the oven to 325°F.
Cover the potatoes with water and bring to a boil. Salt the water and boil to tender. Drain and return the potatoes to the hot pot; mash with milk and cheddar and season with salt and pepper. Cover to keep warm.
Melt 1 tablespoon of butter in a small skillet over medium-high heat. Add the brats and brown until crisp.
Mix half the brats into the potatoes and reserve the rest to top the potatoes before serving.
Season the chops or chicken aggressively with salt and pepper. Heat the oil in a large, ovensafe skillet over medium-high heat. Add the meat and brown on each side; transfer to the oven to finish cooking through, 12-15 minutes.
Add 1 tablespoon butter to the skillet and melt. Add the apples and onions and season with salt and pepper. Cook to tender-crisp, 7-8 minutes; remove and cover. Add the remaining 2 tablespoons butter to melt, whisk in the flour, 1 minute, then whisk in the cider or hard cider. Add the stock and let thicken. Add in the Worcestershire sauce, syrup and mustard.
Top the chicken or chops with the apples and onions. Serve the potatoes alongside topped with the crispy brats and douse everything in gravy.