The trick is to have very cold butter, and slightly simmering liquid. You put the cold butter in the simmering sauce and stir rapidly. This melts the butter without splitting it from the liquid. You end up with an onctuous, lustruous sauce.

Typically you would use about 30 g (1 tbsp) of butter for about 125 ml (1/2 cup) of sauce, but quantities vary.

Adding a dash of cream to your sauce before adding the butter will help avoiding the butter splitting.

This cut is achieved by first cutting thin slices of vegetable such as carrot, then cutting those slices in long thin sticks (these would be called julienne), and finally cutting into small dices

Usualy the light ingredient is a meringue (beaten egg whites), or whipped cream.

The purpose of folding is to ensure the light ingredient retains its volume and/or raising power.

The best way to fold is to use a large spatula or spoon, put it against one side of the bowl, and drag it towards the bottom and up against the other side. Turn the bowl 1/4 turn and do it again, until the two ingredients are well mixed.

There are some pots dedicated for that very purpose, although they are not necessary. Often a pot with a wide opening, along with a metal bowl, work even better.

Usualy done for roasting meats, you can use a spoon or a baster. This adds flavour to the meat and may help keeping it more moist.

It is used mostly in stocks, marinades and "instant" broths. It can be cut to in large or small pieces, according to the need of the recipe.