Preheat the oven to 325 °F degrees on the convection setting. Mix the cocoa powder and boiling water in a stand mixer bowl with a whisk attachment on low until blended, scraping the sides with a spatula. Add the chopped baker's chocolate and continue to blend on low.
Melt the coconut oil in the microwave for 30 seconds to 1 minute. Add the coconut oil and avocado oil to the mixing bowl. Add the vanilla and peppermint extracts to the mixing bowl and blend until the mixture has cooled slightly.
Crack the whole eggs into a separate bowl and then add to the stand mixer along with the four more egg yolks. Add four cups of sugar to the mixing bowl and blend. Then add the flour baking mix and whisk until just blended. You should have a smooth, silky batter.
Coat an large baking dish with cooking spray or coconut oil (I use gloves or a plastic Ziplock bag to apply the coconut oil so my hands aren't all coated as well). Pour in the batter, no more than 1 inch deep! If it's too deep it may impact the final texture.
Sprinkle a 9-ounce bag of mini white chocolate chips evenly across the top of the batter, and then take a spatula and swirl the batter so that some of the chips are mixed in. Sprinkle on some flaky sea salt (like Maldon) over the top.
Bake the brownies until at toothpick comes out without batter (melted white chocolate is fine!) for around an hour to an hour and 15 minutes. Let the brownies cool for 30 minutes. Then sprinkle a little dusting of powdered sugar over the top and serve!