Spread hazelnut spread on 1 side of each tortilla.
In a large pan over medium heat add 2 tablespoons of butter and let it melt until bubbly. Add 2 of the tortillas with the chocolate hazelnut spread side facing up. Using an imaginary line add 1/3 cup of marshmallows down 1 half of each tortilla, making sure to keep them in a single layer. Allow the tortilla to slightly bubble on the pan and check underneath for a golden, toasted color. Fold the tortilla over to form a half circle and slightly press down to seal. Cook until marshmallows start to melt but don't lose their shape. Transfer them to a cutting board. Repeat with the remaining tortillas.
Meanwhile, put the hazelnuts on a plate. Cut the tortillas in half, then quickly press the opened sides into the chopped hazelnuts. Arrange them on a serving platter and serve immediately.