Trim off the edges of the bread, or you can leave them on if you prefer. Then, use a rolling pin to flatten each slice.
Spread your choice of filling—peanut butter, Biscoff, or Nutella—on one side of each flattened slice. Roll up the bread tightly.
In a shallow bowl, whisk together egg, vanilla extract, sugar, and milk.
Dip each rolled-up bread in the egg mixture, ensuring it's fully coated.
Heat 2 tablespoon of butter in a frying pan over medium heat. Fry the roll-ups in the butter, turning them to cook each side until golden brown and crispy.
Mix 2 tablespoon of granulated sugar with 1 teaspoon of cinnamon in a small bowl.
Roll the freshly cooked French toast roll-ups in the cinnamon sugar mixture. Serve warm, with your favorite toppings or just as they are!