Sift together the flour, baking soda and salt. Using an electric mixer, in a large bowl, beat the butter with 1/4 cup of the granulated sugar and the brown sugar at medium speed until combined. Add the egg and vanilla and beat until pale. Stir in the dry ingredients just until combined. Divide the dough into thirds and wrap in plastic wrap. Shape the dough into 6-inch logs and refrigerate or freeze until firm.