In a bowl, dice the mangoes and mash them until smooth or slightly chunky. You can also blend to your desired consistency.
Transfer the mangoes to a saucepan, then add sugar and lemon juice. Mix well.
Simmer over medium heat for about 30 minutes until it thickens and reduces by a third. Lower the heat when it begins to bubble and stir occasionally to prevent scorching.
Once the jam reaches the desired consistency, remove it from the heat and let it cool slightly.
To check if the jam is ready, take a small amount using a chilled or frozen spoon. It should hold its shape and drip off slowly. The jam will continue to thicken as it cools.
Pour the warm jam into a mason jar or another glass jar with a tight-fitting lid.
Allow it to cool completely at room temperature, then refrigerate for up to a month or freeze to extend its shelf life.
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Notes
Mangoes: Sweet varieties like Manila or Ataulfo mangoes are excellent for making jam. However, you can also use other sweet mango varieties that are not excessively fibrous or stringy.
Granulated sugar: The sugar adds extra sweetness and acts as a natural preservative. Adjust the amount if the mangoes are too tangy or not very sweet.