Saute Onions in Olive oil until golden. Do not turn down the heat.
Slowly add 1 cup of water. Let simmer until onions are caramelized.
On a low to medium heat,(2 to 4 electric stove setting) The fallowing is a suggestive, considering every one likes their BBQ differently. Add the other 1 Cup of Water, 1 Cup Brown Sugar, 1/3 can tomato paste, 1 tablespoon mustard, and about 1 ounce(shot glass) of pickle juice to the caramelized onions.
Let simmer, stirring occasionally to prevent burn.
Now that you have your base, continue to add the remainder of your ingredients one at a time, until you have the flavor and thickness you desire. If you want it to be more sweet just add more Brown Sugar. Too sweet add more mustard or tomato paste. You can play with this recipe all you want, it will still turn out delicious.
After your sauce has developed a nice base and is thickening, (should be about 2 hours of slow stir's and adding extra ingredients, if your sauce is still too thin at this time, let it simmer longer)you can add your meat of choice, mushrooms, tomato's and let simmer a while longer.
For the finalization. Toast some buns, add some cheese, top with lettuce and enjoy! Side of tortilla chips..
You can freeze the sauce for future meals.
Helpful hint. Each time you stir your sauce, try it.. Make sure the flavor is to your taste. You will need to occasionally add water.
Allow the sauce time to thicken and simmer the acidity of the tomato paste out.