Let sweet potatoes cool slightly, cut in half, and scoop out insides into a bowl. Discard the skins. Mix together the sweet potatoes, white sugar, eggs, salt, 4 Tbs butter, evaporated milk, vanilla, cinnamon, cloves, and nutmeg in a bowl until smooth. Transfer mix into a 9x13 inch baking dish. There is no need to grease the baking dish.
Crush pretzels by hand with a potato masher, or by using a food processor, until finely ground. Mix together the sugar and crushed pretzels. Cut in the butter until the mixture is coarse. (Optional: Stir in the pecans.) Sprinkle the mixture over the sweet potatoes.
Bake sweet potatoes mixture in oven for approximately 30 minutes at 325º, or until the topping is lightly browned