blueberry coffee cake

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.

adapted from http://www.alexandracooks.com/2011/06/29/buttermilk-blueberry-breakfast-cake/