Here Myriel and Catherine are being shown how to properly form the sugary crust on a crème brulée.
Linguistic note: "dessert" comes from des sert, literally to "un-serve", from the French verb servir, to serve. That’s why it has two S’s. In contrast, "desert" comes from the French word désert, literally "deserted". So now you should always remember which one has two S’s and which has only one.