Preheat oven to 325 degrees.
Spray a 9 X 13-inch baking dish with nonstick cooking spray and set aside.
In a medium bowl, combine flour, baking powder, baking soda, and salt. Set aside.
In a liquid measuring cup combine buttermilk, lemon juice, and vanilla. Set aside.
In a large bowl add sugar and lemon zest. Using an electric mixer set on medium, beat until mixture is very fragrant 1-2 minutes. Transfer 1/4 cup of the sugar mixture to a small bowl and set it aside. Add butter to the remaining sugar mixture and beat until mixture is fluffy about 2 minutes. Add the eggs, one at a time, mixing after each addition just until combined. Add the egg yolk and mix to combine. Set mixer to low speed and add flour mixture in 3 additions alternating with buttermilk mixture. Mix until ingredients are just blended.
Pour batter into prepared baking dish and smooth out the top. Bake 25-30 minutes or until a toothpick inserted in the center comes out clean. Allow cake to cool in pan set on a wire baking rack for 10 minutes.
Make the glaze by whisking powdered sugar, lemon juice, and buttermilk together until even and smooth. Spread glaze over warm cake then evenly sprinkle the reserved sugar lemon zest mixture over the top. Cool the cake completely before serving at least 2 hours. Serve