Preheat oven to 350 degrees F.
Lightly spray a 9x9" baking dish with cooking spray.
In medium bowl, combine flour, baking powder, and salt. Mix to combine and set aside.
In large bowl with electric mixer, beat together butter and sugar until light and fluffy, about 1-2 minutes.
Add eggs, one at a time.
Add vanilla, lemon zest and buttermilk, beating until combined.
Slowly add in flour, mixing until just combined.
Fold in blueberries.
Pour into prepared pan and bake in preheated oven for 40-45 minutes, until toothpick comes out of the middle clean.
Let cool for 15 minutes.
To make the drizzle, whisk together 1 cup powdered sugar and lemon juice and add more powdered sugar until desired consistency is reached.
Drizzle over warm coffee cake.
Slice and enjoy!