Dulce de Membrillo is a sweet, very dense jelly made from the fruit of the quince tree.Unlike the jellies we are used to eating in the USA, membrillo is dense enough to hold its shape. It is best enjoyed when cut into thin slices and spread over plain toast or toast with cream cheese. Some people prefer to serve it with Manchego cheese which gives it a salty contrast to the sweetness of the membrillo.