01 - Preheat the oven to 375°F. Lightly grease a 2-quart baking dish with butter or nonstick spray.
02 - In a large bowl, gently toss the sliced bananas with granulated sugar, lemon juice, cinnamon, nutmeg, and cornstarch until evenly coated. Arrange the mixture in an even layer across the bottom of the prepared baking dish.
03 - In a medium bowl, whisk together the all-purpose flour, granulated sugar, baking powder, and salt until well combined.
04 - In a separate bowl, whisk the melted butter, egg, whole milk, and vanilla extract until smooth and fully incorporated.
05 - Pour the wet mixture into the dry ingredients and stir with a spatula until just combined. Avoid overmixing to keep the topping tender.
06 - Spoon the batter evenly over the banana filling, spreading it with a spatula almost to the edges. Some fruit showing through is perfectly fine.
07 - Bake for 35 minutes, or until the topping is deep golden brown and the fruit filling is bubbling around the edges.
08 - Allow the cobbler to cool for 10 to 15 minutes before serving. Serve warm on its own or accompanied by vanilla ice cream or freshly whipped cream.