How does it work?
See what happens when you make a béchamel sauce? It's pretty liquid because of all the added milk, but it heats up slowly while you stir regularly, and suddenly bim! The whole thing thickens and your béchamel is there, thick and creamy.
A simple physical thing happened, the grains of starch in the flour, contained in the roux, finally exploded under the effect of the heat, around 60°C, and immediately absorbed a big part of the milk to form a starch, that's the béchamel.
The link with cornstarch is that it can do the same thing, but as it contains only starch (from corn), its binding power is stronger.
Add to that the fact that it doesn't add any taste, and you have a binder that can be used in many recipes, sweet or savoury, and situations of which here are a few.
Soups and veloutés
When you make a soup (a blended soup) of pumpkin for example, there is sometimes a little problem of texture: it settles, vegetable pulp at the bottom of the pan and water on top.
It doesn't change the taste, but it's not a very pretty or pleasant texture, especially if it's been waiting a while.
Solution : Mix 2 tablespoons of cold water with 2 tablespoons of cornstarch, and incorporate this mixture with a blender or a whisk at the end of the cooking time, you will be amazed by the creamy effect obtained.
Dishes in sauce
When you make a dish in sauce like beef bourguignon, coq au vin, or blanquette de veau, you often need to add flour and cook for a very long time uncovered to obtain a thick sauce. Sometimes, frustratingly, it doesn't even thicken (well).
Solution: Same treatment as for the soup, a tablespoon is enough, added by mixing briskly (whisk, spatula), the neutral taste of cornstarch ensures a thick sauce with an unchanged taste.
You want to prepare a sauce with a deglazing (you pour a liquid, wine for example) of the cooking pan, but without using cream?
No problem, deglaze, bring to a boil and whisk in the cornstarch + water mixture, a large teaspoon is enough. Velvety sauce guaranteed.
Catching up with disasters
You have made a custard, for example, and it has dissociated? All is not lost, add 1 teaspoon of cornstarch + water to the mixer.
Replacing the flour
In some preparations, pastries, creams etc. traditionally made with flour, you can very often replace the flour with cornstarch, because flour, in this context of cooking at low temperature, has a tendency to soften the preparation. That's why pastry cream, almond cream, and even some cookies, will be better and easier to make with cornstarch than with flour.
As you can see, cornstarch is your friend, it's always good to have a pack of it in your cupboards, and it can be used in many ways, mainly as a thickener.
The power of cornstarch again: Make this delicious chocolate cornstarch cream with your kids (less than 5 minutes), you'll have a huge success!
To sum up: Cornstarch is an excellent binder in cooking and baking, it can be used in many recipes, but also to make up for small disasters.
