Heat oven to 350 degrees F. Grease baking sheet.
In bowl, beat butter, vanilla, both sugars and espresso on high speed until fluffy, 4 minutes. On low, add eggs; beat well. Add flour, cocoa and salt; beat until blended. Add nuts and chocolate; mix just until smooth. Place heaping tablespoonfuls of dough on prepared pan, spacing 2 inches apart.
Bake in 350 degree F oven 10 minutes or until barely set. Let cookies cool on pan on wire rack 2 minutes. Transfer cookies to rack; let cool. Store in airtight container for up to 3 days. Note: Instant espresso powder available from The Bakers Catalogue, 800-827-6836 or www.bakerscatalogue.com. Makes 2 dozen cookies.