Rhubarb and lemon baked cheesecake

Method

1. To make the rhubarb curd, mix the rhubarb, the 50g golden caster sugar and grenadine in a pan. Heat gently for about 12 minutes or until the rhubarb starts to break down. Remove and purée in a food processor, then return to the pan. Mix the cornflour with a little of the rhubarb purée from the pan to make a paste, then return to the pan, bring to the boil and bubble for a minute. Taste and, if it’s too tart, add 1 tbsp more sugar. In a bowl, whisk the yolks with the butter and rhubarb mixture. Cover and cool completely.
2. Preheat the oven to 180°C/fan160°C/gas 4. To make the base, butter a 22cm x 9cm deep, loose-bottomed sandwich tin and line the base with a circle of baking paper. Drop the digestives into a sealable freezer bag and crush with a rolling pin to fine crumbs. Melt the butter in a saucepan, then add the crushed biscuits. Stir until well coated, then spoon over the base of the prepared sandwich tin, pressing down to ensure a firm, even layer. Chill in the fridge for 20 minutes.
3. To make the cheesecake mixture, beat the mascarpone and cream cheese for 2 minutes with an electric hand mixer until really smooth. Add the sugar and continue to whisk for a couple of minutes more. Beat in the lemon zest and flour, followed by the beaten eggs, a little at a time, then fold through the soured cream.
4. Spoon layers of the cheesecake mixture and rhubarb curd into the tin and ripple the top with a wooden skewer. Bake for 50 minutes until golden with a slight wobble. Turn off the oven and leave inside to cool completely (see tip). Carefully remove from the tin to a serving plate.