Preheat oven to 325 F
Melt butter and semi-sweet morsels over medium heat using a double boiler. Set aside.
Combine flour, cocoa powder, salt, and baking soda in a small bowl
In a large mixer bowl, beat sugar, eggs, and vanilla extract until well combined
Slowly add chocolate mixture and combine
Add flour mixture and mix thoroughly
Stur in espresso morsels
Drop onto ungreased baking sheets by rounded tablespoon
Bake for 8 to 10 minutes or until edges are firm, but center is still slightly soft. Cool on baking sheets for 2 minutes; remove to wire racks to cool completely.