Preheat the oven to 325 F and coat the baking pan with butter and cocoa powder. For easy removal, you can also add a square of parchment paper to the bottom of the pan.

In a medium-sized heatproof bowl (or a medium saucepan), melt butter and chocolate chips in the microwave. It can help to microwave the butter for about a minute first, then add the chips. Heat for 30 seconds at a time, and stir chocolate mixture after each interval. Continue until the chocolate chips are fully melted.

Add the sugar to the melted butter and chocolate mixture and whisk continuously for 1-2 minutes. This will help add that crinkly crust.

Whisk in the cocoa powder and vanilla extract. Mix until incorporated.

Add the eggs and whisk well.

Add the dry ingredients (cornstarch, baking powder, kosher salt, and fresh flour) and whisk just enough to incorporate.

Pour batter into a prepared pan and spread evenly.

Bake for 30-40 minutes. I removed mine at 30 minutes and they were still quite soft in the middle, but they set up more as they cool. For a firmer center, feel free to bake for closer to 35-40 minutes or until a toothpick comes out clean from the center. The top should feel firm to the touch and they shouldn't jiggle if you gently shake the pan.

Allow the brownies to cool completely in the baking pan before removing them. Do not remove them while still warm or they will be too delicate and may crumble.

Once cooled, remove from the pan (invert on a plate or cutting board) then use a sharp, clean knife to cut them into pieces. Serve and enjoy!