Preheat oven to 350°F. Place melted butter in a 9- x 9-inch baking dish.
Gently stir blueberries, lemon zest, lemon juice, and 1/4 cup of the sugar in a large bowl until totally combined.
Whisk together flour, baking powder, salt, baking soda, and remaining sugar in a medium bowl until combined.
Whisk together buttermilk and vanilla in a glass measuring cup. Add buttermilk mixture into flour mixture, and continue to stir until the batter is smooth.
Pour the dough mixture evenly over melted butter. (Do not stir.) Using a slotted spoon, scatter blueberry mixture evenly over batter.
Bake in preheated oven until batter is puffed and slightly golden in the center and dark golden brown around edges, 30-35 minutes. Cool on a wire rack at least 15 minutes. Serve warm with ice cream.