½ cup unsalted butter, room temperature
2 tsp. lemon zest or more — zest from 1 large lemon
1 egg, room temperature
1 tsp. vanilla
2 cups flour (set aside 1/4 cup of this to toss with the blueberries)
2 tsp. baking powder
1 tsp. kosher salt
2 cups fresh blueberries
½ cup buttermilk
Preheat the oven to 350ºF.
Cream butter with lemon zest and 3/4 cup of sugar until light and fluffy.
Add the egg and vanilla and beat until combined.
Mix the blueberries with ¼ cup of flour
Next then whisk together the remaining flour, baking powder, and salt.
Add the flour mixture to the batter a little at a time, alternating with the buttermilk.
Fold in the blueberries.
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 the remaining tablespoon of sugar.
Bake for 35 to 45 minutes.
(Note: Baking for as long as 10 minutes more might be necessary.)
Let cool for at least 15 minutes before serving.