Pre-heat oven to 350. Butter a 13x9 pan and set aside. Melt the butter and sugar together in a small saucepan over LOW heat until totally melted and combined, do not let it boil! Cool this for about 30 minutes, then pour into a mixing bowl.
When confident this is cool enough and will not cook the eggs, add all the eggs to the mixture and beat until incorporated. Add the cocoa powder, espresso powder, sea salt, vanilla, baking powder and mix until well combined. Add the flour and mix until incorporated then add the chocolate chips and mix all until well combined. The batter will be THICK, do not thin!
Pour the thick mixture in the buttered pan and spread evenly. Bake for about 30 minutes (toothpick comes out MOSTLY clean, do not over bake!). The brownies will look moist and mostly set. Cool pan on a wire rack for an hour to ensure they are set.
You will have the moistest, fudgiest dark chocolate brownie that is not too sweet but very decadent. Pairs well with a good vanilla bean ice cream but awesome on their own!