Step 1

Preheat the oven to 350 degrees F (175 degrees C). Grease a baking dish with butter.

Step 2

Place a layer of blueberries into the prepared baking dish.

Step 3

Combine flour, baking powder, and salt in a small bowl. Whisk together buttermilk, eggs, and sugar in a large bowl. Add flour mixture to buttermilk mixture and stir until batter is smooth. Mix in vanilla extract and orange zest. Carefully pour over blueberries in the baking dish.

Step 4

Bake in the preheated oven until set, about 30 minutes. Sprinkle with a thin layer of brown sugar. Return to the oven and bake until sugar is lightly browned, 10 to 15 minutes. Serve warm or cold.