How do I make my food taste like leftovers
I think that your thinking in terms of &quot;leftovers&quot; is what is tripping you up here. Cooking food involves tons of chemical changes, and some of them happen best on the stove, and others need a long period of resting time.
If you have a recipe which tastes better on the second day, then all you have to do is to plan to serve it on the second day. See it as a recipe whose last stage needs 24 hours and happens at fridge tempearature. You wouldn't serve yogurt before it has spent 8 hours at 46 C, because the mixture doesn't taste like yogurt yet. Similarly, you shouldn't serve your &quot;perfect beef stew&quot; before it has spent 24 hours at 4 C, because it doesn't taste like &quot;perfect beef stew&quot; yet.
If you are looking for ways to speed up the process, I don't think these exist. Maturing of foods involves complex chemical reactions, which need their time. This is why many luxury food items let you know how long they were aged.
For a bit of background, see also this question on the process of flavors &quot;marrying&quot;.