Start by melting the butter. You can melt the butter in the microwave or on the stovetop. In a medium-sized saucepan add the butter (which has been at room temperature for 20-30 minutes) and melt in on medium heat swirling the saucepan constantly.
Transfer the butter into a big mixing bowl and let the butter cool to room temperature so it won’t cook the eggs.
Add the cocoa powder, brown sugar, sugar, egg, egg yolk, salt, and vanilla extract to the bowl with the butter and mix with a whisk until well combined.
Sift the flour, add the baking powder and gently mix until the mixture is almost combined.
Add the chocolate chips and fold the mixture with a spatula until just combined, cover the bowl with plastic wrap, and let the dough rest in the fridge for at least an hour. We let the dough rest in the fridge overnight.
Use a cookies scoop to scoop out the cookies or scoop the cookies with a regular tablespoon, 1 ½ tablespoon at a time.
Place the cookie dough balls onto a parchment paper-lined baking sheet, and top with more chocolate chips and bake for 9-11 minutes, depending on the size of your cookies. Let the cookies cool for 5 minutes, and then transfer them to a wire rack to cool completely.
Top each cookie with flaky salt and serve next to a cup of milk for the best experience!