For this 30-minute meal, fry the sandwiches on the stovetop while potatoes and onions roast in the oven. The potato side-dish is delicious with the turkey and cheese sandwiches.
1. Heat oven to 450 degrees F.
2. Place potatoes and onions on a baking sheet and toss with the olive oil. Season with the salt and pepper. Bake at 450 degrees F for 20 minutes or until tender, stirring halfway through cooking time.
3. Meanwhile, place 4 slices of bread on a work surface and spread each with 2 teaspoons of the mustard. Equally divide the turkey and cheese over each bread slice. Top each with 3 pieces of arugula and the remaining bread slices.
4. In a shallow dish, beat eggs, milk, cayenne and nutmeg.
5. Heat a large nonstick skillet over medium-high heat. Add 1 tablespoon of butter; when foamy, dip 2 of the sandwiches in the egg mixture and add to the skillet. Cook for about 3 to 4 minutes per side or until nicely browned. Remove sandwiches from skillet; keep warm. Reduce heat to medium; repeat with remaining butter and sandwiches.
6. Serve the sandwiches immediately with the roasted potatoes on the side.