This is specifically for making sauces, and particularly clever when you are using your own recipes
This mode is ideal when using the Thermomix for your own sauce recipes.
It allows you to cook sauces in your Thermomix without having to guess at how much cooking time to input.
To understand what is going on let me explain the stages.
First it will stir the ingredients gently whilst increasing the temperature to about 60°.
Then, as the temperature rises further and the sauce starts to thicken, the stir speed will increase to keep the sauce nice and smooth.
Finally the speed settles back to a gentle stir and holds the sauce at the thickening temperature (either 80° or 100°C) for a further 4 minutes giving the sauce time to be thoroughly cooked.
All you need to decide is whether your recipe is egg based such as hollandaise, creme anglaise (proper egg custard), lemon curd etc in which case choose the 80° option.
Or is your sauce thickened with flour such as a creme patissiere, bechamel sauce (what you might call white sauce), custard with added corn flour, or cheese sauce, in which case choose 100°.
Once you understand it you can apply this mode to so many of your own recipes.
When making a sauce that would generally start with a roux you can of course do that part first by cooking the butter and flour for 4 minutes at 100° speed 2, then add the milk and set to Thicken Mode to finish it. Equally you can put the ingredients all in together without first cooking the roux and you will get a very much quicker version of the same sauce but not made in the classic way.
***I think that it is useful to understand that this mode works by reaching a temperature and then holding it it whilst the blades stir at a speed fast enough to have a nice smooth sauce. Therefore it is not working by reducing the sauce. It is also not suitable for thickening dishes which have elements which you do not wish to be broken up, e.g you couldn't thicken a stew or a curry as the ingredients would get pulverised by the speed of stirring***