In an electric mixer on high speed, cream together the 6 tablespoons of sour cream, butter, sugar, and salt. Turn the mixer off. Scrape down the bowl, and return the mixer to high speed. Add the vanilla and the egg and combine thoroughly. Scrape down the bowl again. Sift the flour and baking soda together into a separate bowl. Turn the mixer to low speed and gradually add the flour mixture until just combined. Wrap dough in wax paper and refrigerate for 30 minutes. Preheat oven to 375°F. Using a 1 ounce ice cream scoop, place the dough balls onto an ungreased cookie sheet, spacing them approximately 2 inches apart. Place the cookie sheet into the center of the oven and bake for 18 to 20 minutes or until cookies are golden brown. Immediately place the cookies on a cooling rack. Allow them to cool completely before storing. To serve, dollop with sour cream; 3/4 cup should be enough for all cookies.  

Serving suggestion: For additional flavor, replace vanilla extract with almond or mint and/or add citrus zest to dough. Sugar the tops of the cookies before baking for extra crunch.