A year ago, the New York Times published this recipe for cola syrup.
I won't bother posting an illustrated step-by-step recipe since this blog already did a much better job of that than I could.
I've made a couple of batches attempting to add kola nut to the recipe. The kola nut that I get (from this source) is hard as a rock, and boiling for 20 minutes wasn't sufficient to extract much. So I start simmering the kola (2 Tablespoons) in 3 1/4 Cups water for 20 minutes, than I add the rest of the ingredients:
zest of 2 Oranges
zest of 1 Lemon
zest of 1 Lime
2 tsp Fresh Ginger
1 inch Vanilla Bean (split)
1/2 tsp Lavender
1/2 tsp Citric Acid
1/8 tsp Star Anise (one point)
1/8 tsp Nutmeg
1/8 tsp Cinnamon
and simmer for 20 minutes more. The resulting tea is difficult to strain; after straining the big stuff out, the rest won't go through a coffee filter. The best I could do was let the particulates settle in the fridge overnight and gently decant all but the settled out bit the next day.
Next, I returned the tea to the stove to add the sugar. For each cup of tea, I added 1 1/2 oz. of brown sugar, and 10 1/2 oz. of white sugar (i.e. I put 3 Tablespoons of brown sugar in a measuring cup, and fill to the 1 1/2 cup line with white sugar).
At this stage, the recipe also calls for caramel color, but I was unable to find any of that. This step is optional and can be skipped, but I still decided to color it with regular food coloring (4 drops of black, 8 drops red, 12 drops yellow) which worked just fine.
I made a Rum and Coke with 3 Tablespoons rum, 3 Tablespoons cola syrup and filled the rest of the glass with soda water.
If I had ordered a rum and coke at a bar and they served me this, I would be convinced that the bartender used spiced rum, and accidentally started pouring ginger ale in it before noticing their mistake and switching to cola. It's a tasty beverage, but nobody would confuse it for a typical rum and coke.