Buttermilk-Blueberry Breakfast Cake

1. Preheat oven to 350 degrees. Cream butter with the lemon zest and 7/8 cup of sugar until light and fluffy. 2. Add the egg and vanilla, and beat until combined. Meanwhile, toss the blueberries with 1/4 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" square baking dish with butter or coat with non-stick spray. Spread batter into pan. Sprinkle with remaining Tbsp. sugar. Bake for 35 min. Check with a toothpick for doneness. If necessary, return pan to oven for a few more minutes. Let cool at least 15 min. before serving.