Beat together shortening, butter, brown sugar, egg, and vanilla
in medium bowl (I actually use my Kitchen Aid
stand mixer for this... it helps to keep my hands free for other things...) until light and fluffy, about 3 minutes. Mix in flour, baking soda, and salt. Be sure to add the flour about 1/2 cup at a time and mix in between additions. Cover bowl with plastic wrap and refrigerate about 45 minutes.