1Beat butter in a large mixing bowl with an electric mixer on medium to high speed for 30 seconds. Add the brown sugar, cocoa powder, baking soda, and salt. Beat until combined, scraping sides of the bowl occasionally. Beat in egg, sour cream, and vanilla until combined. Beat in as much of the flour as you can with the mixer. Stir in remaining flour along with chocolate chips using a wooden spoon. Refrigerate dough at least 1 hour.
22. Heat oven to 350 degrees F. Place powdered sugar in a small bowl. Form dough into 1 ½ inch balls, roll in powdered sugar. Place balls 2 inches apart on air-bake cookie sheet sprayed with cooking spray. Bake for 8 to 10 minutes or until edges are firm. DO NOT OVERBAKE! Cool on baking sheet for 2 minutes, transfer cookies to wire rack and cool. Makes about 32.
3Helpful hints and variations:
Place in layers separated by waxed paper in an airtight container; cover. Store at room temperature up to 1 week or freeze up to 3 months.
1 tsp. cinnamon and/or coffee powder may be added. Finely chopped pecans or walnuts are good additions, too.