Prep the Guavas: Wash and peel the guavas. Cut in half, scoop out the seeds, and strain them to collect the juice. Blend the flesh until smooth.
Cook: In a large, heavy-bottomed pan, mix the guava pulp, sugar, and water. Add lemon juice and vanilla extract or cinnamon if using. Cook over medium-low heat, stirring constantly to prevent sticking or burning.
Consistency Check: Once the mixture thickens and darkens in color, test for readiness by spreading a small amount on a plate. If it wrinkles when nudged, it’s ready.
Cool and Set: Pour the hot guava paste into a shallow dish lined with parchment paper. Smooth the top with a spatula and let it cool at room temperature. Once set, cut into desired shapes.
