For the banana strudel, preheat the oven to 180 °C. Melt the butter. Spread a thin layer of melted butter on one sheet of strudel dough, preferably with a brush.
Place the second pastry sheet on top. Roughly chop the chocolate and the nuts, cut the bananas into slices.
First spread the bananas on about 2/3 of the strudel dough, then sprinkle with the chocolate and nuts.
Fold in the two wide sides of the strudel and roll up the strudel. Place on a baking sheet and brush with the remaining melted butter.
Bake for 30 minutes until golden brown. Serve the banana strudel still warm sprinkled with powdered sugar.