1. Preheat oven to 350°F (175°C) and butter a 9×13-inch baking dish.

2. If using fresh sweet potatoes, peel, chop, and boil until tender. Drain and mash; if using canned yams, drain and mash.

3. In a large bowl combine mashed sweet potatoes, melted butter, brown sugar, granulated sugar, eggs, milk, vanilla, cinnamon, and salt. Mix until smooth and slightly fluffy.

4. Spread the sweet potato mixture evenly in the prepared baking dish.

5. In a separate bowl stir chopped pecans, brown sugar, flour, and cinnamon. Pour in melted butter and mix into a coarse crumble.

6. Sprinkle the pecan streusel evenly over the sweet potato base without pressing down.

7. Bake for 35 to 40 minutes until edges bubble and topping is golden brown. For extra crisp, broil 2 minutes, watching closely.

8. Allow casserole to rest 10 minutes before serving to let layers set and topping firm up.

9. Store leftovers covered in the refrigerator up to five days. Reheat in a 300°F oven for 10–15 minutes to preserve crunch.