Trim the crusts from each bread slice, then flatten each slice with a rolling pin until thin and even.
Place about 1 to 2 teaspoons of your chosen filling (softened cream cheese, Nutella, and/or diced strawberries) about 1 inch from one end of each flattened slice and roll up tightly.
In a shallow bowl, whisk together the eggs and milk until combined.
In a separate shallow bowl, stir together the granulated sugar and ground cinnamon.
Heat a skillet over medium heat and melt about 1 tablespoon butter to coat the pan.
Dip each roll-up in the egg mixture, coating it completely, then place seam-side down in the skillet. Cook in batches, turning to brown all sides, about 2 minutes per side; add more butter to the pan as needed.
Transfer cooked roll-ups directly to the cinnamon-sugar mixture and roll each until evenly coated.
Serve warm; optionally offer syrup for dipping.