Reprinted with permission from Cooper Boone
4 tablespoons unsalted butter cut into 4 pieces, 8 tablespoons melted and cooled
1 ½ cups sugar
3 teaspoons grated lemon zest
4 cups blueberries
1 ½ cup all purpose flour
3 teaspoons baking powder
3/4 teaspoon salt
1 ½ cups whole milk
1. Place oven rack in middle position. Heat oven to 350 degrees. Place 4 tablespoons cut-up butter in baking dish and transfer to oven. Heat until butter is melted, 8 to 10 minutes.
2. In food processor, pulse 1⁄4 cup sugar and lemon zest.
3. Roughly mash blueberries in bowl and set aside.
4. Combine flour, 11⁄4 cups sugar, baking powder, and salt in large bowl. Whisk in milk and 8 tablespoons melted, cooled butter until smooth. Remove from oven, transfer to wire rack, and pour batter into prepared pan.
5. Dollop mashed blueberry mixture unevenly (in random clumps) over batter. Evenly sprinkle lemon sugar, and bake until golden brown and edges are crisp, 45 to 50 minutes, rotating pan halfway through baking. Let buckle cool 30 minutes. Serve warm.