Preheat your oven to 350°F (175°C). Melt the stick of butter and pour it into a 9×13-inch or 9×9-inch baking dish.
In a mixing bowl, whisk together the flour, baking powder, salt, and sugar.
Stir in the buttermilk, vanilla extract, and lemon extract until the batter is smooth and well combined.
Pour the batter evenly over the melted butter in the baking dish. Do not stir.
Spoon the lemon pie filling over the top of the batter. Again, do not stir.
Bake at 350°F for 30-35 minutes in a 9×13-inch dish (or 45-50 minutes in a 9×9-inch dish) until the top is golden brown and set.Optional topping: Beat egg whites, sugar, and vanilla extract until stiff peaks form. Spread over the baked cobbler and broil until lightly browned. Let cool slightly before serving.