Cook butter in a saucepan over medium heat until melted. Remove from heat and cool for just a minute.
Whisk in sugar and cocoa powder until combined.
Whisk in flour, salt, vanilla and eggs. Mix just until combined.
Gently Fold in the espresso chips.
Spread into a greased 8 x 8 inch baking pan. Bake at 350 degrees for 18 - 20 minutes.
Work quickly while making these brownies because you want the butter warm but not hot. If it is too hot the eggs will scramble when you add them. I cooked these for 18 minutes. They were slightly underdone, just how I like them. If you prefer them to be a little more on the done side, cook them for 20 - 22 minutes. While these are good room temperature, a quick 10 - 15 second warm up in the microwave makes them taste like they just came out of the oven!