Preheat the oven to 350°F. Grease an 8x8 pan and line with parchment. Set aside.
Start by adding 2 sticks of unsalted butter to a heavy bottomed saucepan. Melt it over medium heat. If you want, continue heating it until the butter has browned. Here's our guide for how to brown butter for step-by-step instructions! The key is, no matter if you're browning the butter or not, the butter needs to be hot enough to melt the chocolate easily! After the butter is nice and hot (and potentially browned) remove the saucepan from the heat and add in 30g of cocoa powder and 100g of chocolate chips or chocolate pieces. Keep mixing everything together with a rubber spatula to melt the chocolate and combine everything until smooth. Once combined, remove from the saucepan and place in a separate container to cool.
In a large bowl, using an electric mixer, mix together the eggs, the egg yolk, 125g of white sugar, and 125g of light brown sugar until pale and fluffy. This will take 3-4 minutes.
Once the chocolate has cooled down, stream it in slowly to the egg and sugar mixture while using the hand mixer on medium speed to incorporate it. Be sure to scrape the bowl a few times with a rubber spatula to make sure everything is incorporated.
Next, add in 1 tablespoon of vanilla extract, 2 teaspoons of apple cider vinegar, and 2-3 teaspoons of red gel food coloring to achieve the desired color. Mix on medium speed until completely combined.
Now, slowly sift in ¾ cup of all purpose flour and 1 teaspoon of kosher salt to the wet ingredients. Mix the batter on low speed with the electric mixer to incorporate gently. Once almost all the way mixed, switch to a rubber spatula to ensure you don't overmix the brownies at this stage. Scrape the bowl and make sure everything is completely incorporated.
Transfer to your prepared baking pan, and bake for 30-40 minutes(for us, 35 minutes is about perfect), until the top is set and a toothpick comes out mostly clean with a few moist crumbs. Don't overbake! The brownies will continue to bake in the hot pan as they cool.
Set the pan on a cooling rack and allow them to cool completely before cutting into them.