Preheat oven to 350º F.
Cook and peel the sweet potatoes (or use canned sweet potatoes that have been drained, heated and mashed).
Add butter and beat in the sugar while the potatoes are still hot.
In a separate bowl, beat eggs, add evaporated milk, then combine with the sweet potato mixture.
Add the cinnamon, nutmeg, lemon juice and vanilla. Mix until smooth.
Pour into the unbaked pie shell - make the topping. Melt butter then add the brown sugar and nuts,
cooking slowly for 2 - 3 minutes. Allow this to cool, then sprinkle over the pie filling.
Bake 40 - 45 minutes. Let cool before serving, good with lightly sweetened whipped cream.