Drain sweet potatoes,melt butter and beat eggs. In large bowl mash sweet potatoes with potato masher. Add sugar, beaten eggs, 1/2 cup melted butter, and vanilla extract. Beat with mixer till well combined. Pour into a sprayed 9x13 baking pan. Set aside.
In medium bowl combine brown sugar, flour, and nuts.Blend together with hands. Add 1/3 cup melted butter and kind of lightly toss with fingers to combine. You want it crumbly.
Sprinkle over sweet potato mixture and bake 25 minutes in 350 degree oven or till golden brown on top. Allow to set for a couple of minutes before serving.