Pre-heat oven to 350F degrees. Line a 9x5 baking pan with parchment paper and set aside.
In a large skillet melt butter. Add chocolate chips and whisk until it starts to melt. Remove from heat and continue to stir the chocolate until completely melted and smooth.
Add both sugars and fold with a spatula until the sugar has been fully absorbed.
Add in eggs, one by one and mix to combine.
Now add the vanilla, sea salt and give it a quick stir.
Finally add in flour and cacao powder by pouring both into a sifter and sifting flour and cacao powder into the brownie batter. This will avoid batter from clumping up. Stir until creamy and smooth
Pour brownie batter into baking pan. Top with marshmallows (as much or as little as you like) and bake for 25-27 minutes. It’s done when toothpick inserted comes out clean around the edges and wet-ish when inserted into the middle.
Remove from oven and allow it to cool off for 5 minutes. Then use the parchment paper to lift the brownie on to a serving platter. Cut into bite size pieces. Serve with graham crackers and extra marshmallows