Line a 9 x 13 pan with foil so that foil hangs over the edge. Spray with cooking spray.
In a mixing bowl, beat together butter and both sugars. Beat until light and fluffy.
Add in egg, vanilla, orange extract and orange zest. Mix to combine
Add in flour, baking powder, cornstarch and salt. Mix until combined. Dont' overmix.
Spread dough evenly into prepared pan and bake for 20 minutes or until edges are just lightly golden brown. Cool completely.
Orange Frosting
With a mixer, cream butter. Add in sugar and all other ingredients. Mix until combined and creamy and a good spreading consistency. If too thick, add in some additional milk, if too think, add in some extra powdered sugar.
Spread on cooled cake. Sprinkle with orange zest or chopped sugared orange.