In a large bowl or stand mixer, beat mashed sweet potatoes, sugar, eggs, milk, softened butter, salt, cinnamon, and vanilla until smooth.
Transfer mixture to a buttered 2-quart baking dish.
In a small bowl, mix brown sugar, pecans, oatmeal, and flour. Cut 2 tablespoons of cold butter into mixture until crumbly.
Bake, uncovered, for 45-50 minutes, or until the top is golden brown and crispy and the potatoes are heated through.
A pastry blender is the best tool for cutting butter into dry ingredients. You can also use a stainless steel dough scraper if you do not have a pastry blender handy. Put your dry ingredients onto a flat surface, such as a cutting board. Then, use the scraper blade like a chopper, cutting through ingredients and mixing as you go until the dry ingredients are crumbly and everything is well combined.
Recipe by Lynnette Sheppard at https://www.lynnettesheppard.com/sweet-potato-bake/