Cook bacon to crisp: skillet, air fry or oven (whatever your preferred method). RESERVE 1 tablespoon of bacon fat, rough chop the bacon and set it aside.
Make the brown sugar topping: In a medium microwave safe bowl, melt butter. Stir in flour, brown sugar, cinnamon, salt, diced pecans and most of the bacon, leaving some for the garnish. Set aside.
Peel and dice potatoes into about 1 1/2″ cubes. Addo large pot of cold water. Bring to a boil, season with salt and cook over medium heat until fork tender (about 15 minutes). Cook time will vary with size of potatoes. Drain potatoes and return them to a same pot.
Turn up the heat up under the pot for 15-30 seconds to remove any excess moisture. Add butter, letting the heat from the potatoes melt it. Pour in about half of the milk and all of the bacon fat, cinnamon, vanilla and brown sugar. Use a potato masher to mash potatoes to your desired consistency - add remaining milk as needed.
Butter an approximately 9×9″ or similar size baking dish. Transfer mashed sweet potatoes to the baking dish smoothing the top.
Sprinkle brown sugar topping over the potatoes. Bake 15-18 minutes at 375 degrees or until golden. Add remainng bacon to the top. Broil 1 minute to recrisp the bacon (watch closely so it doesn't burn!). Remove from the oven, sprinkle with fresh parsley (optional) and serve warm.