Step 1

In a large mixing bowl, whisk together the melted butter, brown sugar, and granulated until evenly combined. The mixture should resemble a paste, like wet sand. This takes 1-2 minutes.

Step 2

Add the egg, egg yolk, and vanilla extract to the bowl. Whisk thoroughly until smooth.

Step 3

Pour the gluten-free flour, cacao powder, and salt into the bowl. Mix gently until the ingredients are just combined. Be careful not to over mix the batter! It will be quite thick. Set the bowl aside while you make the blondies.

Step 4

Preheat the oven to 350°F and line an 8x8" square baking pan with parchment paper. Leave some parchment paper hanging over the sides to make it easy to remove the brownie blondies later.

Step 5

In a separate large bowl, whisk together the melted butter, brown sugar, and granulated sugar until it resembles a sandy, paste-like texture.

Step 6

Add the egg, egg yolk, and vanilla extract to the bowl. Whisk until smooth and creamy.

Step 7

Pour the gluten-free flour and salt into the bowl. Mix gently until just combined. Again, be careful not to over mix the batter.

Step 8

Use a measuring cup or large spoon to scoop about 1/4 cup of brownie batter into two opposite corners of the pan (diagonal from each other). Then, scoop about 1/4 cup of blondie batter into the remaining two corners of the pan, also opposite each other. (See process pictures in the blog post for clarity).

Step 9

Next, add a scoop of brownie batter on top of the corners with the blondie batter. Add a scoop of blondie batter on top of the corners with brownie batter. Repeat this process, adding brownie batter over blondie batter, and vice versa, until all the batter is gone. Think of it like creating a checkerboard pattern.

Step 10

Use the back of a spoon or a spatula to gently "swirl' the top layer of the brownie blondies to create a marble pattern. Be careful not to swirl too much, or the mixtures will blend together and not have a distinctive marble pattern!

Step 11

Bake for 40-45 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs. Allow the bars to cool in the pan for 30 minutes. Then, use the edges of the parchment paper to lift the brownie blondies out of the pan.

Step 12

Once cool, slice into 16 square bars. Serve and enjoy!