Preheat oven to 350°F. Line an 8x8 inch square baking pan with parchment paper (keep the sides hanging off so that you can lift the bars out of the pan). Spray with cooking spray and set aside.
In a medium bowl, whisk together the flour, baking powder, and salt.
In the bowl of a stand mixer fitted with the paddle attachment, or in a large bowl with a handheld mixer, beat the butter and sugar together until creamy and fluffy.
Add the egg, vanilla extract, and lemon extract. Beat until well combined.
Add the dry ingredients to the wet ingredients and mix until just combined. Do not overmix. A few streaks of flour are ok.
Transfer dough to the prepared pan and press into the pan using your hands or a spatula. Be sure to press all the way into the corners.
Bake for 20-25 minutes, or until the edges are slightly golden.
Remove from the oven and cool on a wire rack in the pan before frosting. Frost with vanilla frosting.