Sift together the flour, baking soda, and salt. Using an electric mixer on medium speed, combine the butter, sugar, eggs, and vanilla. Add the sour cream and mix well. On low speed, gradually add the flour mixture until well blended. Turn the dough out onto a lightly floured board, and pat with floured hands to a ¼-inch thickness. Cut with a 2-inch round, floured cookie cutter and place on cookie sheets about 1 inch apart. Bake for 10 to 12 minutes, until the teacakes are lightly browned. Do not overbake. Using an egg turner, remove the cookies to a rack to cool.