Spread the 2 tablespoons nutella over the bottom half of each croissant.
Top the nutella with the bananas, and then the top of the croissant.
In a skillet or heavy pan, melt the butter and a pinch of salt and gently cook over medium heat until browned.
Add the croissants to the pan and cook until crispy on both sides and the nutella is melted. I gently pushed down on the sandwiches squishing them together. If you need to cook in batches, then repeat.