Sprinkle the short rib with salt, pepper and 1/2 teaspoon of the espresso. Heat 1 tablespoon of the oil in a saute pan over high heat. Sear the rib on all sides to golden brown. Remove the rib to an oven-safe pan.
Add the bacon to the hot pan and cook until lightly browned. Add the onions and continue to cook until the onions begin to brown. Add the chicken stock, brown sugar and the remaining 1 tablespoon espresso, and then bring to a boil. Add the bacon mixture to the short rib, then cover and cook for about 3 hours.
Remove from the oven. Carefully remove the rib from the pan and pour the rest of the contents into a blender and puree. Strain the puree into a bowl, add the ketchup, and whisk together to make the BBQ sauce.
In a separate bowl, combine the mustard greens, apple, cabbage and fennel. Mix the remaining 1 tablespoon oil, the vinegar, honey, 1/2 teaspoon pepper and a pinch of salt. Dress the slaw with the dressing and mix well.