Preheat electric oven to 350°F. In large bowl of electric mixer, cream butter and sugar. Add eggs and vanilla; beat well. Sift flour with cocoa, baking powder, and salt; gradually add to creamed mixture. Add nuts and chocolate chips.
On a lightly floured board, knead dough until smooth. Divide dough in half and form into 2 logs about 10 x 3-inches. Place logs on an ungreased baking sheet, 3 inches apart.
Bake for 25 to 30 minutes or until tooth pick inserted in center comes out clean; cool. Reduce oven temperature to 325°F.
Cut logs into eighteen 1/2-inch diagonal slices, place slices on baking sheets and bake for about 10 minutes on each side. Cool.Servings: 36 slices