Preheat oven to 350° F. Line a 9" x 13" pan with parchment paper so that two opposite sides have an overhang. This will allow you to lift the bars out once they are cooled, to make clean cuts. If ultra clean cuts are not a big thing for you, simply spray the pan lightly with a non-stick spray. Set pan aside.

In a large bowl, whisk together flour, sugar, baking powder, and salt. Add lemon zest (my favorite zester!) and whisk again to separate and coat all the little pieces of zest. Set bowl aside.

In a small bowl, whisk together butter, eggs, lemon juice, and vanilla.

Add wet ingredients to dry ingredients and stir until combined. Spread batter evenly in prepared pan. Bake for about 20 minutes, or until a toothpick inserted in the center comes out clean. The lemon bars should spring back lightly when gently pressed. Remove from oven and let cool completely on a wire rack.

In a small bowl, whisk together all glaze ingredients until smooth.

Drizzle glaze over top of cooled lemon bars and then use a spatula or the back of a spoon to spread glaze evenly over the bars.

Place pan in refrigerator for 2 hours.

Run knife around the perimeter of the pan where there is no parchment paper and then lift the bars from the pan using the parchment paper overhangs. Cut into squares. I think these bars are best enjoyed when chilled, but feel free to serve them at room temperature also.