Preheat and prep: lightly grease a 9" x 13" metal pan, line it with a parchment sling, then grease the parchment paper as well. Preheat oven to 350°F.*1
Whisk together most blondie ingredients: combine melted butter, brown sugar, sugar, vanilla, and eggs and mix by hand or with a mixer on low until everything is fully incorporated into a smooth and creamy mixture.
Add flour: blend together flour, baking powder, and salt in a small bowl. Blend the dry mixture into the batter by hand until fully incorporated.
Transfer to pan and level: transfer batter to prepared pan, and spread into an even layer all the way to the edges. Place pan in fridge to chill while you prep the brownie batter.*2
TO MAKE THE BROWNIE BATTER:
Melt chocolate and butter: over a double boiler or in the microwave, melt butter and dark chocolate chips together, mixing until fully combined, shiny, and smooth.*3 Allow chocolate to cool for 5-10 minutes (really hot chocolate could cook our eggs in the next step).
Combine sugar and eggs: whisk together sugar, eggs, and vanilla until smooth.
Add chocolate: add slightly cooled chocolate mixture to the egg mixture and mix until fully combined.
Add flour: blend together flour, baking powder, and salt in a small bowl. Blend the dry mixture into the chocolate batter by hand just until fully incorporated.
Pour into pan: remove the blondie pan from the fridge.*4 Carefully drop brownie batter in a bunch of large spoonfuls spread evenly across the top of the chilled blondie batter. Use a spatula to gently spread the brownie batter into a solid layer until it fully covers the blondies. (These two batters are a little soft and may mix up a little, in which case, don’t worry! They’ll still taste just as delicious.)
Bake: bake for 36-42 minutes, until the surface of the bars looks dry and fully set, nothing moves when you gently shake the pan, and a toothpick inserted into the center comes out clean.
Cool to room temperature: cool bars fully before using the parchment sling to transfer the bars to a cutting board to slice (or simply slice them right in the pan). Pass out a couple of bars to share some sweetness, and enjoy this scrumptious chocolate + vanilla mash-up!
Test Kitchen Tips
*1Can you make these bars in an 8” square pan? While technically you can make a half batch and significantly reduce the baking time for an 8" square pan, I found the texture and look was much nicer in a 9" x 13" pan, so I'd recommend sticking with the full batch size for best results.
*2Save some dishes! After finishing the blondie batter, just give your tools a quick rinse (no need to sanitize) as you can use that same bowl and those tools to mix the brownie batter instead of dirtying new ones.
*3Melting Chocolate: if using the microwave to melt your chocolate, set it to 50% or lower power and heat for 30-second intervals, stirring well between each round, to prevent the chocolate from burning.
*4Make sure blondies are fully chilled: if you're really speedy mixing up your brownie batter, and notice your blondies are still pretty soft, just re-chill them in the fridge, or even the freezer for another 10-15 minutes before topping with the brownie batter.
Storage: store air-tight at room temperature for up to a week.You can freeze baked bars, but they’ll lose some of their fudginess in the thaw and are best enjoyed fresh.
⭐ Did you bake up this tasty recipe? ⭐Please give it a ⭐ rating in the recipe card or leave a comment at the bottom of the page to help others find this sweet recipe. I’d love it if you'd share your treats (literally and electronically!), and tag @mint.and.mallow.kitchen on Instagram or Facebook so I can see your beautiful bakes! Xo, Jocelyn