Preheat toaster oven or regular oven to 375 degrees.
Spray an 8 inch square pan with cooking spray.
Roll out the sheet of crescent dough and cut it in half.
Fit one of the dough sheets into the pan.
Warm ⅓ cup of Nutella for 30 seconds in the microwave to make it easier to spread.
Spread the Nutella onto the dough.
Top with 20 marshmallows halves.
Cover with second sheet of crescent dough.
Bake for 12-15 minutes or until the top starts to brown. If it starts to brown too soon, cover with foil.
Remove from oven and top with remaining ⅓ cup Nutella and 12 marshmallow halves.
Return to oven for a few minutes until the marshmallows have started to brown.
Let cool and serve warm.