• Preheat the oven to 350ºF degrees and line an 8-inch square baking dish with parchment paper; set aside.

Make the Cookie Dough:

• In a medium saucepan, melt the butter over medium-low heat. As the butter melts, it’ll start to foam, then turn a clear golden color. Continue to stir the butter, scraping up any browned specks from the bottom of the pan as it starts to brown. It should have a nutty aroma.
• Once browned and nutty, turn off the heat and allow to cool for 5 minutes.
• Whisk in both sugars, the egg, and vanilla until smooth. Switch to a wooden spoon, add the flour and baking powder and stir until just combined. Fold in the chocolate chips. Transfer dough to another bowl and return the pan to the stove.

Make the Brownie Batter:

• In the same saucepan over medium heat, melt the butter, then stir in the cocoa powder until smooth and glossy. Remove from the heat and stir in the sugar. Add the egg and vanilla, stirring until fully incorporated. Stir in the flour and salt, followed by the chocolate chips.
• Alternate spooning the brownie batter and cookie dough into the pan, smoothing out the top. Bake for about 30-33 minutes, or until edges are firm and golden. Cool in pan for at least 20 minutes before cutting.