First hull the strawberries, then put them in a colander and rinse them briefly with cold water.
rain well and dry them on kitchen paper before transferring them to a food processor or liquidiser. Blend them to a smooth purée, then stop the motor, add the sugar and blend again very briefly. After that add 1 pint (570 ml) water and the lemon juice, blend once more, then pour everything into a fine nylon sieve set over a bowl.
Rub the purée through the sieve, then pour it into the polythene freezer box, cover with a lid and put into the freezer for 2 hours. By that time the mixture should have started to freeze around the sides and base of the container, so take a large fork and mix the frozen mixture into the unfrozen, then re-cover and return it to the freezer for another hour.
After that repeat with another vigorous mixing with a fork, cover again and re-freeze for a further hour. At this stage the mixture should be a completely frozen snow of ice crystals, and is ready to serve. It can remain at this servable stage in the freezer for a further 3-4 hours, but after that the ice will become too solid and it will need putting in the main body of the fridge for 30-40 minutes or until it is soft enough to break up with a fork again.
I like to serve the granita in small, narrow, unstemmed glasses – but any wine glasses will do so that the sparkling colour can be seen in all its glory.