Wash the plums thoroughly under cool running water. Cut each plum in half and remove the pits, carefully chopping the plums into small chunks while keeping the skins on for better texture and pectin.

In a large heavy-bottomed pot, combine the chopped plums with granulated sugar, lemon juice, and water. Stir until evenly mixed and let sit for 15–20 minutes.

Heat the mixture over medium heat, stirring frequently to prevent sticking. Once it boils, reduce to a gentle simmer for 20–30 minutes, stirring every few minutes until thickened.

To test doneness, use the cold plate method: place a spoonful of jam on a cold plate and tilt; if it wrinkles and holds shape, it's ready. If not, cook for an additional 5–10 minutes.

Remove the pot from heat, allow to cool slightly, then carefully spoon hot jam into clean jars, leaving a little space at the top. Cool completely before sealing for refrigeration or follow canning methods for longer storage.