Heat a heavy bottomed stock pot over medium heat on the stove top until warm. Add the bacon all at once and stir frequently. Cook until the bacon is crispy and until all of the liquid in the pan is foamy and bubbling (see video if you aren’t sure what this means).
Remove the bacon from the pan to a paper towel covered plate and set aside.
Pour the bacon grease into a metal container or shatter proof glass container and set aside.
Add two tablespoons of the bacon grease and the 2 tsp of butter to the stock pot and set it back on the stove. Reduce the heat to medium low. Add the onions all at once and add 1 tsp of salt.
Cook on medium low until the onions begin to look translucent (this will take about 10 minutes).
While the onions are cooking, chop bacon up into small bits and set aside.
When the onions appear translucent, stir in brown sugar, sherry vinegar, the cola, the bourgon, 1 tsp of thyme leaves, black pepper and cayenne pepper into the onions. Add the chopped bacon bits into the onion mix and continue to cook over medium low heat until a dark brown color results and the mixture is as thick as jam. This takes at least another 10 minutes but depending on the water content of the onions and other products, could take up to another 25 minutes.
Remove from the heat, stir in the remaining thyme and add the balsamic and olive oil, stir well. Serve warm.