Heat the oil in a large, heavy pot over medium heat and saute onion and garlic until soft. Lower heat, add sugar, syrup, bourbon, vinegar, spices, and cocoa, and reduce for 5 to 10 minutes. Cut the chiles in half and add to the pot, along with the ketchup, water and salt. Cook slowly for 1 1/2 hours, covered, stirring occasionally and adding more water if the sauce becomes thicker than ketchup. When sauce has cooled slightly, puree in the blender. Refrigerated, the sauce will keep 2 to 3 weeks.