Using a potato peeler or sharp paring knife, peel the guavas making sure to remove only the thin skin covering it. Discard the skins.Cut the guavas in halves and scoop out the seeds with a teaspoon. Reserve the pulp for use in a later step.
2. Boil seeds
In a saucepan, combine the guava seeds, cinnamon, cloves, and anise plus 6 cups of water.Boil for ten minutes over medium heat or until the seeds separate, and the water turns a caramel color.Strain the liquid and discard the seeds, but extract as much as you can of the pulp between the seeds. Return the liquid to the pot.
3. Boil the pulp
Add the peeled guavas you had saved to the pot with the liquid, add sugar, salt, prunes, and vanilla, and heat over low heat. Boil until the guava halves are soft, adding water if necessary to keep them from drying out.Once the pulp is soft, and you obtain a slightly thick syrup, remove it from heat and cool to room temperature.
4. Serve
Serve: Remove the spices. Chill in the refrigerator before serving.