Cut your butter into 1 inch slices and combine with espresso chips in a microwaveable bowl. Combine and melt for 10 seconds, repeating as necessary until the butter and chips are fully melted and glossy. Set to the side.
In a large bowl beat the eggs and add the sugar and vanilla extract. Once incorporated add the chocolate-butter mixture and mix well.
In a separate container combine the flour and the baking soda and incorporate into the brownie mixture slowly while stirring.
Preheat the oven at 350°.
Pour your brownie mixture into a greased 8-inch square baking tray and bake for 30 minutes at 350° or until cooked through.