Mom's Sweet Potato Casserole

This is my mom's recipe, so it is genuine southern sweet potatoes!
-2 sweet potatoes, peeled and cubed (Not yams, yes there is a difference. Sweet pototes are the more yellow ones, not orange)
Cook for 20 min. and mash. Then add:
-1/4 cup butter
1/2 cup sugar
1 egg
1/8-1/4 cup of milk
1/2 tsp vanilla

Mix together the following for the topping:
1/2 cup butter
1/4 cup flour
1/2 cup brown sugar
1/2 cup chopped pecans
1/4- 1/2 cup coconut
Pour potatoes into a baking dish (probably 9x13) and cover with topping. Bake 25 min. at 350.