Preheat the oven to 425°. Add butter to a 9x13-inch baking dish and place it in the oven for 5 minutes or until the butter has melted.
In a blender, add the eggs, milk, flour, salt, vanilla, and sugar. Blend for about 1 minute, until the mixture is bubbly. Pour the batter into the warmed baking dish and immediately bake for 20 minutes, until the pancake is lightly browned and puffed.
In a small bowl, combine the hazelnut spread and milk, microwaving for 15-20 seconds, until warmed, then stir to combine. When the pancake is done, top with sliced bananas, the hazelnut mixture, and powdered sugar. Slice and serve immediately.