Spread softened cream cheese on one side of each slice of bread. Add dulce de leche or Nutella if you want an extra indulgent filling. Sandwich two slices together and repeat for the remaining bread.
Whisk eggs, milk, vanilla extract, cinnamon, and salt in a shallow bowl until smooth.
Dip each stuffed sandwich into the custard mixture, ensuring both sides are coated without becoming soggy. Let each slice soak for a few seconds on each side.
Heat a skillet or griddle over medium heat and add butter. Cook the sandwiches for 2-3 minutes on each side, or until golden brown and crispy. Add more butter as needed.
Mix granulated sugar and cinnamon in a shallow bowl. Press each warm French toast into the cinnamon sugar mixture to coat evenly.
Slice the stuffed French toast diagonally and serve warm. Top with maple syrup, whipped cream, or fresh fruit for extra sweetness.