½ cup unsalted butter, room temperature
2 teaspoons lemon zest or more – zest from 1 large lemon
7/8 cup + 1 tablespoon sugar*
1 egg, room temperature
1 teaspoon vanilla
2 cups flour (set aside 1/4 cup of this to toss with the blueberries)
2 teaspoons baking powder
1 teaspoon kosher salt
2 cups fresh blueberries
½ cup buttermilk**
* This 1 tablespoon is for sprinkling on top
** To make homemade buttermilk, place 1 tablespoon of vinegar or lemon juice in a liquid measuring cup. Fill cup with milk until it reaches the 1-cup line. Let stand for five minutes. Use only 1/2 cup of the prepared mixture for the recipe.
Preheat the oven to 350 degrees. Cream butter with lemon zest and 7/8 cup of the sugar until light and fluffy. 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. 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 remaining tablespoon of sugar. Bake for 35 to 45 minutes. Check with a toothpick for doneness. If necessary, return pan to oven for a couple more minutes. (Note: Baking for as long as 10 minutes more might be necessary.) Let cool at least 15 minutes before serving.
