Preheat oven to 350° and line an 8x8 baking dish with parchment paper and grease with butter or cooking spray.
In a microwave safe bowl melt together butter and chocolate in 20 second increments, stirring each time, until smooth and completely melted. Set aside to cool slightly.
In a mixing bowl beat together sugar and eggs with either a stand mixer or an electric handheld mixer until fluffy and combined, 2-3 minutes.
With the mixer on low add in the chocolate and butter mixture and vanilla and mix until combined.
In a separate bowl combine salt, flour and cocoa powder.
Add dry ingredients to wet ingredients and fold together with a spatula. Add in chocolate chips and fold until just combined.
Pour into prepared baking pan and bake in the center rack of the oven for 20-22 minutes until the center is just set and the top is shiny.
Let cool completely before slicing. Store in an airtight container for 2-3 days.