In a large microwave-safe bowl, combine butter and sugar. Microwave for 30 seconds, then remove and stir with a whisk. Repeat process 4 more times. Though granules of sugar will remain, the goal is to get the mixture to a glossy finish.
Add in eggs one at a time, whisking in between each addition. Whisk vigorously until the mixture lightens in color slightly. Add the vanilla extract and mix well.
Add in cocoa powder, flour, and salt and fold until just combined. Last add in the chocolate chips and fold to combine.
Transfer the mixture into the prepared baking pan and bake for roughly 25 minutes, testing for doneness by inserting a knife into the center of the brownies beginning at 20 minutes. You’ll know they’re done when the edge is set, but a knife inserted into the middle still comes out with a bit of brownie batter on it. It might take up to 35 minutes for them to cook through depending on your oven!
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Notes
If you would like to make these in a 9 x 9-inch pan you can just double the recipe!
Make sure you’re using a high quality cocoa powder. I’ve made the with both Dutch processed cocoa powder as well as natural. I prefer to use Dutch processed as it has a smoother, deeper flavor, but natural will also work if it’s all you have on hand.
Be careful not to over bake your brownies. When you insert a knife into the middle you’ll want it to come out a little gooey as the brownies will continue to bake as they cool.