01 -
Preheat oven to 350°F (175°C). Place the stick of butter in a 9×9-inch baking dish and melt in the oven as it preheats, about 3-4 minutes.
02 -
In a large bowl, whisk together flour, baking powder, salt, and sugar. Add buttermilk, vanilla extract, and lemon extract (if using). Stir until the batter is smooth and well combined.
03 -
Pour the batter evenly over the melted butter in the baking dish. Do not stir them together.
04 -
Spoon the lemon pie filling or lemon curd evenly over the batter. The filling will sit on top but will sink during baking.
05 -
Bake in the preheated oven for 45-55 minutes until puffed up and golden brown around the edges. The center should be set but slightly soft, and a toothpick inserted should come out clean or with a few moist crumbs.
06 -
Remove from the oven and let cool for 10-15 minutes to allow the filling to set slightly.
07 -
Cut into squares and serve warm. Optionally top with whipped cream, ice cream, powdered sugar, or fresh lemon slices.