2 pounds yams, peeled, cut into 1-inch pieces
1/2 Cup butter
1 Cup sugar
1 teaspoon vanilla

Sweet potato topping:
1 cup brown sugar
1/2 cup flour
1/2 cup melted butter
1 cup pecans
1/3 cup milk
1 teaspoon vanilla

Peel and boil yams in a large pot until soft, about an hour. (Yams take longer to cook than russet potatoes.) Drain and mash. Transfer to mixing bowl. Add butter. Using electric mixer, beat until smooth. Add sugarand vanilla. Beat to blend. Pour into prepared baking dish.
Prepare topping:  Blend topping ingredients to a consistency of wet cookie dough. Drop by spoonfuls evenly on top of yams. Connect the dollops to create a smooth topping.  Bake 35 minutes at 350 degrees until brown and crusty.