Heat oven to 350F. Grease and flour bottom of 9-inch square baking pan; set aside.

Heat saucepan of water over medium-low heat until hot but not boiling. Combine butter, dark chocolate chips and unsweetened dark chocolate in bowl; place over saucepan of hot water. Cook, stirring occasionally, until chocolate is melted. Remove bowl from saucepan; set aside to cool slightly.

Combine sugar, eggs, instant espresso powder and vanilla in bowl; mix well. Stir in cooled chocolate mixture until combined.

Add flour, baking cocoa and salt; stir until just combined. (Do not over mix.)

Pour into prepared pan. Bake 25-30 minutes or until toothpick inserted into center comes out clean and brownies begin to pull away from sides of pan. Allow to cool completely before cutting.