Wash and clean the strawberries and remove the stalks. Place in a large bowl and pour sugar over them. Let it steep for a few hours (6-8 hours or overnight), stirring carefully from time to time so that the fruits are not damaged. Bring to the boil in a stainless steel saucepan (never use enamelled dishes!) On medium heat while stirring, let simmer for 5 minutes, switch off the hob (leave the saucepan on it) and slowly let it cool down completely. Repeat process. Bring to the boil for the third time, let it boil for 5 minutes and pour into the clean jars (or jars with screw caps) while still hot. Immediately turn the glasses upside down, cover them with a wool or quilt and let them cool down completely (takes approx. 24 hours). Russian jam does not become as firm as German, the consistency is like a thick syrup. 1 kg of strawberries makes about 800-850 ml of jam.