Preheat your oven to 350°F (175°C). Peel and cube the sweet potatoes into roughly equal pieces to ensure even cooking.
Place the cubed sweet potatoes in a large pot and cover with cold water. Bring to a boil and cook until tender when pierced with a fork, about 15-20 minutes. Drain well using a colander.
Transfer the drained sweet potatoes into a mixing bowl. Add brown sugar, milk, melted butter, vanilla extract, cinnamon, and salt. Mash everything together until smooth and creamy using a potato masher or electric mixer.
In a small bowl, combine chopped pecans and crumbled turkey bacon. Have mini marshmallows ready if using.
Spread the sweet potato mixture evenly in the baking dish. Sprinkle the pecan and turkey bacon mixture evenly over the top.
Bake in the preheated oven for 20-25 minutes, until the topping is golden and slightly crispy.
If using marshmallows, remove the dish about 5 minutes before baking ends. Sprinkle mini marshmallows evenly on top and return to oven. Bake an additional 5 minutes or until marshmallows are puffed and lightly browned.
Remove from oven and let cool slightly before serving. Enjoy your Sweet Potato Casserole with Pecans!