Place potatoes in large saucepan or pot. Cover with water and add a dash of salt. Boil until fork tender for mashing.While potatoes cook, chop bacon into bite size pieces and cook until crisp or your preference of doneness. I cook mine over medium to medium-low heat in order to really render the fat.Remove bacon and set aside. Pour off grease if you have more than a tablespoon or 2. Alternatively, if you used really lean bacon, you may need to add some olive oil for the next step.Add onion and garlic, if desired, to remaining grease and cook until crisp-tender, 2-5 minutes.Add chopped cabbage or slaw mix and cook until desired crispness (or lack thereof), 6-15 minutes.When potatoes are done, drain and then add back to the hot pot over low heat to make sure they are dry.Add butter and warmed milk or cream and mash as usual.Add salt and pepper to taste.Stir in the bacon and cabbage/onion mix.Test again for seasoning.Place in serving dish and enjoy!Note that the traditional way to enjoy colcannon is with a well in the center of the bowl filled with melted butter, thus the optional butter listed above. I usually skip this step since I add the butter to the dish itself, but enjoy it however you like!