½ cup unsalted butter, room temperature 2 tsp. lemon zest or more — zest from 1 large lemon 7/8 cup* + 1 tablespoon sugar** 1 egg, room temperature 1 tsp. vanilla 2 cups flour 2 tsp. baking powder 1 tsp. kosher salt 2 cups fresh blueberries ½ cup buttermilk
* 7/8 cup = 3/4 cup + 2 tablespoons ** This 1 tablespoon is for sprinkling on top
1. Preheat the oven to 350ºF. Cream butter with lemon zest and 7/8 cup of the sugar until light and fluffy.
2. Add the egg and vanilla and beat until combined. Meanwhile, toss the blueberries with ¼ cup of flour, then whisk together the remaining flour, baking powder and salt.
3. Add the flour mixture to the batter a little at a time, alternating with the buttermilk. Fold in the blueberries.
4. Grease a 9-inch square baking pan (or something similar) with butter or coat with non-stick spray. Spread batter into pan. Sprinkle batter with remaining tablespoon of sugar. Bake for 35 minutes. Check with a toothpick for doneness. If necessary, return pan to oven for a couple of more minutes. (Note: Baking for as long as 10 minutes more might be necessary.) Let cool at least 15 minutes before serving.