Mix flour, cocoa, espresso, baking soda, salt and pepper in a bowl and set aside. Beat sugar and oil in a medium bowl at medium speed until well blended. Beat in sour cream, egg and vanilla. Beat in flour mixture until soft dough forms. Form into ball. Refrigerate 3-4 hours, or until firm. Put powdered sugar in a shallow bowl. Cut into 1-inch pieces and roll into a ball, then roll in powdered sugar. Use ungreased cookie sheets. Bake 10-12 minutes at 350°F until cookies are firm to touch. Don’t overbake. Cool on wire racks.