Spread 1 teaspoon of Dijon mustard on 8 sourdough slices. Top with evenly divided Swiss cheese, turkey, pluots and remaining bread slices.
Whisk together eggs and milk until thoroughly combined.
Heat 2 tablespoons butter in a large nonstick skillet over medium heat. Dip two sandwiches in the milk mixture, transfer to the skillet and cook until golden brown, 2-3 minutes per side. Repeat with remaining sandwiches. Garnish with powdered sugar, if desired.
