So, cooking food does not increase its caloric value beyond that of the combined ingredients.
If you throw a bunch of asparagus and a blob of lard in a skillet, you end up with much higher calorie asparagus - but no more than actually went in the skillet to start with, it just took up a lot of the lard calories.
Cooking can reduce the number of calories in a food (esp if you burn it) - but it can also reduce the number of calories required to digest the food by breaking up some of the tougher chemical bonds ahead of time. This can result in a net caloric gain for the person eating it, even though the foodstuff itself hasn’t gained calories. I don’t think this would ever be more than a modest % gain however, unless the stuff you started with was virtually inedible.
So sure, cooking a hard to digest meal like acorns or highly fibrous wild vegetables might improve the net caloric value for eating them, but not all that much. For the most part, what you get out == what you put in, 'cause thermodynamics applies to chemistry and biology just as much as it does to physics.
Taste and general palatability, of course, are a whole different ball game. Cooking can improve those as much as one cares to imagine — though of course flavor is in the taste buds of the beholder.
