Roughly chop half the strawberries and whizz the rest in a food processor or with a stick blender to a purée.
In a big bowl, stir the condensed milk into the puréed strawberries then gently stir in the yogurt until well mixed. Fold through the chopped strawberries.
Scrape the mixture into a loaf tin or container, pop on the lid or wrap well in cling film and freeze overnight, until solid. Remove from the freezer about 10-15 mins before you want to serve the frozen yogurt. Can be frozen for up to 1 month.