Swap out your all-purpose flour for cereals – crushed sugar frosted flakes, + real (not instant or quick) oatmeal + some sort of meusli. Skip the sugar and add dried fruits or fruit leather. More calories and will taste a lot better.
Why cornstarch? Not sure what purpose it serves as you don’t have anything that needs thickening or being prevented from sticking. And if that’s what you are using it for, I’d substiture 1/2 to 2/3 cup brewer’s yeast which will also give you nutritional density.