Trim the crust from the bread. Flatten each slice with a rolling pin. Place a heaping teaspoon of Nutella (or your preferred filling) in the middle of each slice of bread. Spread it evenly, leaving a 1/2-inch border all around. Roll up the bread slices and repeat with the remaining slices. In a shallow bowl, whisk together the eggs and milk. In another shallow bowl, combine the sugar and cinnamon. Warm a griddle or large sauté pan over medium heat. Once hot, melt 1 tablespoon of butter. Dip each roll into the egg mixture, then place it seam side down on the griddle. Cook for about 1–2 minutes per side until golden brown. Add more butter as needed for the second batch. Place the cooked rolls into the cinnamon-sugar mixture and roll them until completely covered. Gently shake off any excess. Serve the French Toast Roll Ups with a drizzle of maple syrup, if desired.