cupish of ketchup (we use store brand, comparable to Heinz), Brown sugar to taste (probably at least half a cup, though 50/50 makes a good mix here). Healthy dose of vinegar, Worcestershire to taste (this for me is a good bit, tablespoonish? and use Lea and Perrins or go home). BBQ rub is a standard BBQ Rub, I use Reichlan's http://www.epicurious.com/recipes/food/views/Basic-Barbecue-Rub-242244 or whatever I put on the meat.
A Turkey baster or two of meat drippings if available for depth.
Put all of this into a sauce pan and simmer until the color is dark brown/maroon, 20-60 minutes