Sift flour, baking soda and salt. In separate bowl, cream butter, peanut butter, brown sugar, and ½ of the granulated sugar. Beat till creamy, then add egg and vanilla. Add dry ingredients, mix on low, just until blended. Place remaining ½ C sugar in a bowl. Shape dough into 1-inch balls, using a heaping teaspoon for each. Roll balls in sugar and place 1 inch apart on un-greased baking sheets. Bake 8-10 minutes @ 350F. Remove from oven and gently press a chocolate kiss into the center of each cookie. Return to oven and bake 2 to 4 minutes longer, until cookies are lightly browned. Cool cookies on wire rack.