Clean and carefully wash strawberries. Remove all damaged or rotten parts. I recommend mixing forest and ordinary strawberries (1:1).
Add sugar and let it stay in sugar 3-4 hours in a large pot. Stir occasionally and wait until fruit removes juices.
Cook in the same large pot for 15 minutes making sure not to burn sugar. Stir always.
After 14 minutes, add fresh juice of 2 lemons. Remove the foam and put the jam in hot (100°C) glass-bottle.
If you like more firm jam, add pectin (usually available in grocery stores). Pectin is added 2 minutes before it is done because pectin looses its characteristic if you cook it too long. Close the hot glass-bottles and keep it in dark place.