1. In a shallow bowl or pie plate, whisk the eggs and milk together. Spread 2 slices of the bread with the Nutella, about 2-3 tablespoons per slice. Place the other slices of bread on top and gently press them together. Carefully dip both sides of each sandwich into the egg mixture until well coated.
2. In a large skillet, melt the butter. Add the French toast sandwiches and cook until golden, about 4 minutes per side. Cut the sandwiches in half on the diagonal and transfer to plates. Drizzle with syrup and dust with powdered sugar and serve immediately.