COOKIE DOUGH: In a mixing bowl, cream butter and sugars. Add egg and vanilla, beat until light and fluffy. Combine dry ingredients, beat into creamed mixture. Divide dough in half, place each half between two sheets of waxed paper. Roll into 12 x 10-inch. rectangles. Chill until almost firm, about 30 minutes.
FILLING: In a saucepan over low heat, melt chips and butter. Add vanilla and salt, mix well. Spread over dough. Carefully roll up each rectangle into a tight jelly roll, wrap in waxed paper. Chill for 2 hours or until firm.
Cut into 1/8-in. slices with a sharp thin knife, place on greased or parchment lined baking sheets. Bake at 350° for 7-10 minutes or until lightly browned. Cool on wire racks.