Preheat the oven to 180°C. Grease a 23cm silicone ring mould well with non-stick spray.
1. Purée: Put the ingredients in a saucepan, bring to the boil, then simmer slowly, stirring occasionally, for 20 minutes or until a purée forms. Set aside to cool.
2. Cake: Cook the pears in the rooibos until soft, then chop finely. Add the apples and lemon zest and juice.