Mash or sieve the strawberries and stir with the sugar. Leave for 20 minutes, stirring occasionally, then add pectin and stir for 3 minutes. Put into small containers, cover and seal. Leave for 5 hours at room temperature, then put into refrigerator until jelled. This may take 24–48 hours. Store in freezer. Thaw for 1 hour at room temperature before serving.