Mix together all dry ingredients: flour, cornstarch, baking powder, baking soda, salt, cinnamon, ginger, allspice, and nutmeg
Combine vegetable oil and dark brown sugar
Add eggs, egg white, sour cream, and vanilla extract to the wet mixture
Fold in grated carrots
Combine wet and dry ingredients
Fill cupcake liners and bake according to recipe instructions
For frosting: Beat softened cream cheese and butter together
Add powdered sugar, vanilla extract, and salt to frosting
Frost cooled cupcakes and top with crushed walnuts if desired
