Add the potato chunks to a large pot and cover with cold water. Bring the potatoes to a boil and cook until they are fork tender, about 20 to 30 minutes. While the potatoes are boiling, heat a large skillet over medium-low heat and add the chopped bacon. You have 2 options here: you can cook the bacon until it is totally crispy or you can cook it about 3/4 of the way, so the fat has rendered, and then pop the dish in the oven and let the bacon finish crisping up there. Either way, you want all of the fat to be cooked out.
Remove the bacon with a slotted spoon and place it on a paper towel to drain. Remove about 1 tablespoon of bacon fat from the skillet and set it aside in a bowl. To the same skillet, add the butter and heat it over medium heat. Add the sage leaves and cook until they are crispy, about 1 to 2 minutes per side. Remove them with a slotted spoon and place on a paper towel to drain.
At this point, the potatoes are most likely finished, so drain the thoroughly and add them back to the pot. Mash them with a fork or potato masher, then use a whisk or electric hand mixer to whip them. Once whipped, add in the reserved bacon fat, the milk, the bourbon and the brown butter. Whip the potatoes again until everything is combined. Taste the potatoes and add the salt and pepper, seasoning more or less if desired.
If serving the potatoes immediately, spread them in a dish and top them with the crispy bacon. Crumble the sage on top. If you’re waiting a bit to serve them, heat the oven to 325 degrees F and top the potatoes with the bacon. Bake them for 25 to 30 minutes, then remove them from the oven and crumble the sage over top.