Combine sugar, brown sugar, and butter. Blend until smooth. Add vanilla, egg, and Shamrock Farms sour cream. Mix until mixture is slightly fluffy. Add flour, salt, and baking powder and blend until all ingredients are combined.
Melt chocolate chips in microwave safe bowl. Microwave on high, stirring every 20 seconds, until melted (note – chocolate chips will melt in approx. 60 seconds). Fold melted chocolate into cookie mix. DO NOT MIX. Gently combine chocolate and cookie mix to give a swirled / marble pattern. Drop by rounded spoonful onto ungreased cookie sheet.