Sweet Potato Cupcakes, Muffins and Cake

Ingredients

• 2 1/2 cups flour
• 15 ml baking powder
• 1 ml salt
• 5 ml cinnamon
• 5 ml grated nutmeg
• 1 1/2 cup sugar
• 1 1/2 cups oil
• 4 egg yolks (keep the whites, they get used as well)
• 60 ml hot water
• 2 cups grated sweet potato
• 1 cup chopped walnuts (optional)
• 5 ml vanilla
• 4 egg whites (stiffly beaten)