Preheat oven 400º. Line a jelly roll pan with aluminum foil and brush with melted butter.
Sift together flour, cocoa, espresso powder, and salt into a bowl; set aside.
In large bowl, cream butter, and sugar beat on high speed about 2 minutes. Beat in eggs, sour cream and vanilla. Add warm chocolate mixture and flour mixture all at once and beat on low speed until just blended. Fold in nuts.
Spread in pan. Bake 20 to 25 minutes.
Let cool, cut into 2 inch squares.
Recipe submitted by Nick on 12/30/99