Prep the cinnamon sugar by mixing granulated sugar and cinnamon in a small bowl.
Lay a flour tortilla flat and spread 2 tablespoons of chocolate hazelnut spread in the center, leaving a 2-inch border. Add ½ cup mini marshmallows on top.
Place a tostada shell or handful of corn chips over the marshmallows for crunch.
Fold the tortilla edges inward to fully enclose the filling, forming a sealed parcel. Place seam-side down. Repeat with the second tortilla.
Heat a skillet over medium-low. Brush the top with melted butter, sprinkle with cinnamon sugar, and place sugar-side up on the skillet. Cook 3–4 minutes until golden.
Flip, brush the other side with butter, sprinkle cinnamon sugar, and cook 3–4 more minutes until crispy and gooey inside.
Transfer to a board, let cool 1 minute, then slice and enjoy warm.