1Preheat oven to 350 degrees
Mix oil and sugar with an electric mixer until smooth. Add the egg yolks one at a time beating after each addition
2Sift the flour, baking powder, salt, cinnamon and nutmeg together. Add the boiling water and mix. Add the four mixture to the oil and egg mixture and mix. Add in the vanilla. Fold in the grated sweet potatoes. In a separate bowl, beat the egg whites until they are stiff and form peaks. Gently fold the egg whites into the batter until blended.
3Prepare three 9" cake pans b lining the bottoms with parchment paper or wax paper and spraying them well with nonstick baking spray. The type that contains flour works best for this. Take my advice and do not skip this step! This cake is very moist and can stick or the layers can break if you do not line your pans. Divide the batter evenly among the pans and bake for 25 to 30 minutes. A pick inserted in the center should come out clean.
4Remove from oven and allow to cool before turning onto a cake plate.
Prepare frosting when the cakes have cooled by combining the evaporated milk, sugar, butter, egg yolks and vanilla in a saucepan over medium heat. Cook for about 12 minutes, stirring constantly or until the mixture has thickened.
Remove from heat and add coconut. Beat until cool and thick and spreading consistency.
Frost between layers of cake, top and down the sides. Garnish the top with the nuts. The consistency will be similar to the frosting you use on German Chocolate Cake.