Strawberries rinse, hull and drain well. Bring water with juice of one lemon to a boil and cool repeatedly. Put the strawberries in a high saucepan and mash them, pour the lemon water and leave with the lid closed for one night.
Stir occasionally. Then filter through a muslin cloth and squeeze the fruit residue with it. After about 8 hours, with a whisk (or blender on low speed), stir the sugar until completely dissolved. Fill into bottles and seal.