The basis of a large number of hot tunks and soups is roux / roux. Flour with butter as light yellow or possibly brown roasted, cold liquid added and the sauce cooked under continuous stirring. Only you take to the sauce less liquid, than to the soup, because it must be thicker than this.
Light sauce: butter and flour are roasted until light yellow, then the cold liquid is added.
Dark sauce: Ingredients as for the light sauce. Flour and butter are roasted brown before adding the liquid.
Whipped sauce: The sauce is prepared in a water bath, i.e. a high saucepan is placed in a second one with boiling water. The egg yolks are mixed with water, then the butter is added one piece at a time, beating continuously, until the sauce is thick and fluffy. Do not let it get too hot, so that it does not curdle. If it coagulates, it can sometimes be saved by taking it out of the water, adding 1 tsp of cold water and beating again.
Mayo: To the egg yolks, add the salt and then the oil drop by drop, stirring or beating continuously. Stir until the mixture is thick and fluffy. In between, you can add the juice of a lemon drop by drop. Cut two small triangles in the stubble so that the oil drips. The bottle can be placed on a tin can covered with a folded dishcloth,