01 - Preheat oven to 350°F (180°C). Lightly grease a 9x13-inch (23x33 cm) baking dish.
02 - Place sweet potato chunks in a large pot and cover with water. Bring to a boil, reduce heat, and simmer for 15 to 20 minutes until tender. Drain thoroughly in a colander.
03 - Mash the hot sweet potatoes in a mixing bowl until smooth. Stir in bourbon, milk, melted butter, brown sugar, eggs, vanilla extract, cinnamon, and salt. Blend until mixture is creamy and fully incorporated.
04 - Pour sweet potato mixture into the prepared baking dish. Use a spatula to smooth the surface evenly.
05 - Combine flour, brown sugar, cold diced butter, cinnamon, and salt in a bowl. Cut butter into dry ingredients using a pastry cutter or fork until coarse crumbs form. Fold in chopped pecans.
06 - Distribute pecan streusel evenly across the sweet potato base.
07 - Bake for 25 to 30 minutes, or until topping is golden brown and the casserole is heated through.
08 - Allow casserole to rest for several minutes before slicing and serving.