Simple syrup is a pastry chef’s basic. It is equal parts water and sugar. You simmer both to a syrup (5-10 minutes) and then add in a bit of flavor if you like (such as vanilla) or not. This syrup is brushed on the cake surface BEFORE icing them. It ensures your cakes are moist and tender, versus a dry, hard surface that the icing just sits on. It doesn’t make things too sweet. It makes them stay fresh and perfectly moist. It’s, as they say, simple.