In a large bowl, use an electric hand mixer to cream together 3/4 cup butter, white sugar, and brown sugar until smooth. Beat in egg and vanilla. In a separate bowl, combine flour and salt. Beat dry ingredients into the creamed mixture just till slightly combined. Finish by mixing with a wooden spoon to form a soft dough. Roll dough into 1 inch balls, and place balls 2 inches apart on parchment paper lined or ungreased cookie sheets. Make an indention in the center of each cookie using your thumb or index finger.