Using a mixer. The recipe calls for mixing everything in a standing mixer or a hand-held mixer. I truly believe this is important if you care about shiny, crackly brownie tops! Mixing by hand. However, you can also mix everything by hand!  I recommend whipping the eggs by hand with a wire whisk, and then whipping them again after you add the sugar. I have opted to make these the lazy way, with no whipping and just mixing as follows: melt the chocolate chips/butter (or coconut oil) together. Then add the other wet ingredients and stir until combined. Then add dry ingredients and stir! It's easy, but usually ends in funky-looking tops but the brownies still taste amazing.