Method
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1
Put the sugar, vanilla, lemon zest and 200ml/7fl oz water into a small saucepan and slowly bring to the boil, stirring occasionally, until the sugar has dissolved. Simmer gently for 5 minutes until slightly thickened. Remove from the heat and leave to cool.
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2
Put the strawberries in a food processor or blender and whizz until smooth. Pour the purée into a bowl, add the yoghurt and crème fraîche and mix until smooth. Strain the sugar syrup into the mixture and whisk to combine.
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3
Pour into a ziptop bag, squeeze out all air, and seal. Freeze, lying flat, until solid. Remove from freezer and break into chunks small enough to fit into the bowl of your food processor or a high-powered blender. Pulse until completely smooth. Put in a container and back in the freezer
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4
Transfer the frozen yoghurt to the fridge to soften for 20 minutes before serving.