It's natural to assume that there is no such thing as a mistake, that mistakes are merely opportunities to learn. Indeed, the notion of unlimited second chances informs much of the way we think about ourselves and the world.
And yet sometimes there's no going back. In cooking, the point of no return is generally after heat has been applied. Over-seasoning is also nearly irreversible and doesn't even require actual cooking to happen.
But for the most part, once food has been heated, chemical changes have occurred that make it impossible for those ingredients to revert to their previous state. In other words, you can cook something, but you can't uncook it. And you especially can't unburn it.
You Can't Unburn Something
Overcooking is by far the most frequent cause of most common cooking mishaps (including what most people would refer to as "burning," where visible scorching or blackening occur), and is simply a result of the item getting too hot. (Or cooking it too long, which is effectively the same thing.)
Obviously, scorching and blackening can render a dish inedible, to the extent the burnt parts can't be removed. Like a soup or sauce that has scorched on the bottom causing the burnt flavor to permeate the entire thing.
In other cases, you might be able to get away with trimming away the burnt bits if they're confined to the edges, like with a pie crust or cake. With something like a roast, if the outside is blackened, the inside is likely overcooked as well. So you can trim away the burnt exterior, but you still need to decide what to do with the overcooked but still technically edible other parts. You can't fix it, so you might have to just eat it the way it is.
You Can't Unseason Something
With the latter two, you can to some extent balance things out with other flavors, but there is no way to remove salt, sugar or spice from a dish once it's in there. Your only recourse is to dilute the seasoning by adding more of everything else.
For instance, if you're making a soup or a stew and you discover you've added too much salt, the way to fix it is by essentially making a double batch of whatever the recipe is. Obviously you might need to go shopping again, so you need to decide how badly you want to fix it versus just serving it (or serving something else instead).
You Can't Unbreak Something
Sometimes one of the changes that occurs during cooking is that the thing in question literally cracks or breaks into pieces. This includes sunken cakes, collapsed souffles, cracked cheesecakes and so on. Cake pops, after all, did not just invent themselves.
Cracked cheesecake is one of the most common baking mishaps since it is pretty much the worst thing that can happen to a cheesecake and it can happen for several reasons. As for fixing it, you can't knit it back together. So your options are limited to various methods for covering up the crack.
You CAN Fix a Cracked Cheesecake
The best way of fixing a cracked cheesecake is by making a sour cream topping and spreading it evenly over the top of the cheesecake. You can also accomplish this with fresh fruit or a fruit compote, but sour cream will do the best job of filling in the crack and smoothing over the top.
It helps to let the cheesecake cool for 10 to 15 minutes. You will by now have observed that the top is cracked. Combine two cups of sour cream, 1/4 cup of sugar and a teaspoon of vanilla, and pouring the mixture over the top of the cheesecake while it's still in its springform pan, then pop it back into a 450 F oven for 10 more minutes.
You Can Fix a Broken Sauce
Certain kinds of sauces, like mayonnaise, aioli and butter-based sauces like hollandaise and beurre blanc, are what's called emulsified sauces. An emulsion is what is created when you blend two (or more) different liquids together to produce a single, thicker liquid, without it separating back into its individual components.
With mayonnaise and aioli, it's oil being absorbed into egg yolks. With hollandaise, it's melted butter and egg yolks. With beurre blanc, it's cubes of cold butter being whisked into a reduction of wine and vinegar.
Certain acids, proteins, and starches can help the emulsion to form and to stay together, and the temperatures of the ingredients as well as how rapidly you stir or whisk are also critical.
With that said, things can go wrong. The emulsion can sometimes fail to come together or, as often happens, come together briefly before separating again.
This reseparation is referred to as a broken emulsion, and while it can be dispiriting to see, it is not irreversible.
Fixing a Hollandaise (or Mayonnaise)
Try whisking a tablespoon of boiling water into your broken hollandaise, a drop at a time. If that doesn't work, pull out a new bowl, separate one egg and add the yolk only to the new bowl, then slowly pour in the broken sauce while whisking vigorously.
You can use either of these same two methods to fix a broken mayonnaise as well.
Fixing a Beurre Blanc
With a beurre blanc, since there are no eggs, the technique is similar but different. Instead of hot water, start with a new bowl with a tablespoon of ice-cold water in the bottom and slowly pour the broken sauce into that while whisking vigorously. Alternately you could try whisking some ice chips directly into the broken sauce.