In a grinder add chopped mangoes and make a smooth paste of it and keep it in a bowl.
Now take a wide pan and add mango pulp in it and then add sugar in it.
Keep the flame on medium high, add lemon juice and keep stiring well for 3-4 minutes.
After 4 minutes reduce heat to medium low and cook for 10-15 minutes.
After 15 minutes check the jam. For checking the jam put a small quantity on plate and check if the puree is watery if its not watery that means you jam is ready.
Let jam rest for 2-3 minutes after 3 minutes transfer in a clean, dry air tight glass bottle.