I left the cornflake bag open for too long that it is not crispy anymore. Still taste good, but I wonder what can I do with it.
You can crisp them up again in a hot oven for a few minutes (exact temperature not too important, spread them out thinly on a baking sheet and take them out before they burn). I'd then go on to make a normal cornflake cake recipe of your liking straight away, to avoid having the same problem again.
My solution is close to Chris H except i found this for myself
Take a bit of butter on a pan.
Main point is to use a butter (home butter at best), dont use natural or flower oils that can be bought in a store. That way corn flakes reach nice aroma which natural oils can not reach.
Heat the pan up . After butter gets melt add corn flakes and roast them 3-5min. Dont burn them. You will see that the cornflakes had now slightly different taste because of a butter.
Optionally add salt after you finish roasting.
Thing i should point out.
I have not tried this with "budget" corn flakes since they has different taste and structure against quality ones.