Preheat the oven to 350°F and line a 8x8-inch baking pan with parchment paper.
In a medium-sized mixing bowl, whisk together the flour, baking powder, baking soda and salt. Set aside.
In a large mixing bowl, whisk the brown sugar, granulated sugar, melted butter and eggs for 1-2 minutes until lighter in color and smooth. Add the lemon zest and lemon extract and whisk to combine. Add the dry ingredients to the wet ingredients and stir with a wooden spoon just until no dry spots remain (do not overmix). Pour the batter into the prepared pan and spread it into an even layer. Bake for 24-26 minutes, or until lightly golden and the center is set.
Allow the blondies to cool in the pan for 10-15 minutes. Using the parchment paper, lift them out and transfer to a wire rack to cool completely.
Lemon Glaze
To make the glaze, whisk together the powdered sugar and lemon juice until thick and smooth. Add lemon juice gradually until the desired thickness and texture of glaze is reached. Drizzle or spread the glaze over the cooled lemon blondies. Let the glaze set before serving.
Notes
Fresh Lemon Zest: A non-negotiable that is responsible for the deep lemon flavor.
Lemon Extract: Make sure to use lemon extract and not lemon oil. Lemon extract can also be omitted or substituted for vanilla extract, but the blondies will not have as rich a lemon flavor.
Brown Sugar: Brown sugar is an essential ingredient in blondies and gives them a wonderful butterscotch flavor and adds extra moisture, which keeps the blondies soft and chewy.
Optional Mixins: White chocolate chips, fresh berries, Jimmy sprinkles or a chocolate ganache topping.
Don't overmix the batter after adding the dry ingredients. Overmixed batter can lead to dense blondies.
Err on the side of slightly underbaked for a fudgier blondie. When they are done baking, the edges will be lightly golden brown, and the center will be set, but still slightly soft.
To make this lemon blondies recipe in a 9x13 pan, double the recipe.
Let the lemon blondies fully cool before adding the lemon glaze otherwise, the glaze will melt and become runny.
Measure the flour properly to avoid cakey blondies. Use the spoon and level method. This recipe uses 210 grams of flour.