The Frugal Gourmet's BBQ sauce

1 Tsp salt
1/2 cup white sugar
1/4 cup dark brown sugar
3 cups beef stock
1/2 cup prepared, yellow mustard
1/4 cup white vinegar
1/4 cup liquid smoke
1/2 cup Worcestershire sauce
1/2 cup tomato paste
red pepper flakes, to taste
Combine the above ingredients into a non-reactive sauce pan. Bring the contents of the pan to a rolling boil over a medium flame. Cut the heat to a very slow simmer and reduce until thick - about 1 1/2 hours. Due to the high sugar content, stir often.
Use a liquid smoke that is not "concentrate". On the back of the label, the first ingredient should be "water". If not, use only 1/8 cup.