Preheat oven to 425ºF.
Crush scone or muffin into coarse crumbs in a food processor, using brief pulses.
Melt butter in a 12-inch nonstick ovenproof skillet over medium heat. Add banana slices and cook, tossing gently, until coated all over, 1 minute. Spread bananas in single layer, then scatter on the cinnamon.
Whisk together eggs, milk, flour, sugar, and salt in a medium bowl until only small lumps remain. Pour batter into a pan and cook 1 minute. Scatter on crumbs and transfer the pan to the oven.
Bake until puffed and golden brown, about 15 minutes.
Tip: If you don’t have a 12-inch nonstick ovenproof skillet, melt the butter, pour it into a 1 1/2-quart baking dish, and scatter on the bananas and cinnamon. Pour the batter over the bananas and bake until puffed and golden, 15 to 18 minutes.