3 tablespoons unsalted butter, melted, plus more for the pan
Preheat the oven to 350°. Toast the hazelnuts on a pie plate for 12 minutes, until the skins blister. Transfer the nuts to a kitchen towel and rub to remove the skins. Let cool.
Meanwhile, sprinkle 2/3 cup of the sugar in a large, deep skillet in an even layer. Cook over moderate heat without stirring until a honey-colored caramel forms, about 5 minutes; halfway through cooking, gently swirl the pan to combine the caramel and sugar. Add the banana halves cut side down and cook just until tender, about 2 minutes. Carefully turn the bananas and cook for 30 seconds. Off the heat, add the rum and swirl gently to combine. Cook over moderate heat just until the bananas are tender but not falling apart, about 1 minute longer. Using a slotted spoon, transfer the bananas to a plate.
Add the orange juice and maple syrup to the skillet and boil until slightly thickened, 1 minute. Pour the syrup into a pitcher.
In a food processor, combine the nuts with 1/2 cup of the flour and process until ground. Transfer the mixture to a bowl and add the remaining 1 cup of flour, the baking soda, baking powder and salt. In a small bowl, whisk the buttermilk with the egg yolks and melted butter, then whisk the mixture into the dry ingredients. In a clean bowl, beat the egg whites until soft peaks form. Gradually beat in the remaining 2 tablespoons of sugar until glossy. Fold the egg whites into the batter.
Heat a large nonstick griddle. Brush lightly with butter. Spoon 1/3 cup of batter onto the hot griddle for each pancake. Place 2 banana halves on each pancake and cook over moderate heat until small bubbles appear on the surface. Flip the pancakes and cook until golden, risen and cooked through, about 1 minute longer; lower the heat if the pancakes brown too quickly. Repeat with the remaining batter and bananas and serve the pancakes hot with the orange-maple syrup.