Brown the Butter: Place the unsalted butter in a light-colored saucepan over medium heat. Melt and simmer until golden brown specks develop and it has a nutty aroma, about 5-8 minutes. Pour into a large heatproof bowl to cool slightly.

Combine Sugars: Add the packed light brown sugar and 0.5 cup granulated sugar to the warm browned butter. Whisk for about a minute until well combined.

Add Eggs and Vanilla: Whisk in the room temperature eggs one at a time, followed by the vanilla extract until the mixture becomes smoother.

Mix Dry Ingredients: In a separate bowl, whisk the flour, baking soda, and salt. Gradually add to the wet mixture, gently folding until no flour streaks remain.

Prepare Brownie Mixture: Set aside one-third of the cookie dough. In that bowl, add the cocoa powder, remaining 0.25 cup granulated sugar, and milk, stirring until a thick, fudgy paste forms.

Combine the Mixtures: Fold semi-sweet chocolate chips into the main blondie dough then drop spoonfuls of the brownie batter onto it, swirling gently.

Chill the Dough: Cover and chill the dough in the refrigerator for at least 30 minutes.

Preheat your oven to 350°F (175°C) and line baking sheets with parchment paper.

Scoop and Bake: Using a cookie scoop or tablespoons, portion the dough into balls and place them 2 inches apart on the sheets. Bake for 10-12 minutes until edges are set and lightly golden, allowing them to cool on the baking sheet for 5 minutes before transferring to a wire rack.