Preheat oven to 350 degrees F (175 degrees C). Grease a 9x9-inch casserole dish.
Mix sweet potatoes, white sugar, 1/2 cup butter, milk, eggs, salt, vanilla extract, and cinnamon together in a bowl until smooth; spread into the prepared casserole dish.
Stir brown sugar, pecans, and 1/3 cup butter together in a bowl.
Mix flour into pecan mixture using your hands until evenly coated and crumbly; sprinkle over sweet potato mixture.
Bake in the preheated oven until cooked through and praline topping is lightly browned, about 40 minutes. Cool slightly before serving, at least 25 minutes.