Blondies are all about two things—brown sugar and vanilla—which pair perfectly with lighter, more delicate fruit flavors. Though sometimes overlooked in lieu of brownies, when it comes to adding springy flavors like lemon and blueberry, only one bar reigns supreme, and these dessert bars are proof.
Step 1Preheat oven to 350°. Grease a 9" square baking pan cooking spray. Line with parchment, leaving an overhang on 2 opposite sides. Grease parchment with cooking spray.
Step 2In a medium bowl, whisk brown sugar, butter, vanilla, lemon zest, baking powder, and salt until well combined. Stir in eggs until well combined. Add flour and stir just until combined. Add 3/4 cup blueberries and fold just to distribute.
Step 3Scrape batter into prepared pan; smooth top. Sprinkle with remaining 1/4 cup blueberries.
Step 4Bake blondies until golden and a tester inserted into the center comes out clean, about 35 minutes. Transfer pan to a wire rack and let cool completely.
Step 5In a small bowl, whisk powdered sugar and lemon juice, adding water a few drops at a time, until a drizzling consistency is reached. Drizzle glaze over cooled blondies. Let set 15 minutes.
Step 6Using parchment overhang, lift blondies out of pan and transfer to a cutting board. Slice and serve.