Rhubarb and pistachio millionaires’ shortbread

Method

1. Heat the oven to 180°C/160°Cfan/gas 4 and line the baking tin with baking paper.
2. Using an electric mixer, cream together the butter and sugar for about 3 minutes until smooth and fluffy. Stir in both flours to form a dough. Tip the dough into the baking tin and press down with the back of a spoon into an even layer. Bake for 20-25 minutes until pale gold on top. Meanwhile, roast the pistachios on a small baking tray for 7 minutes until toasted and fragrant. Leave both to cool.
3. Put the rhubarb in a pan with the sugar. Set over a medium heat and cook, stirring, until the sugar has dissolved. Cover with a lid and simmer for about 5 minutes until the rhubarb has broken down. Transfer to a blender, add the lemon juice and whizz to a fine purée.
4. Tip the rhubarb mixture back into the pan and whisk in the vege-gel. Return to a medium heat and gradually bring to the boil, whisking continuously. Simmer for 4 minutes, then pour the rhubarb purée onto the shortbread. It will thicken
   as it cools. Leave it to cool for 30 minutes, then transfer to the fridge for 1  hour to set.
5. Once set, finely chop the pistachios. Melt the chocolate (see Be A Better Cook) and pour it onto the rhubarb layer. Sprinkle over the pistachios while the chocolate is molten. Leave to set at room temperature for about 45 minutes, then score portion lines on top to make it easier to cut later on without cracking the chocolate. Leave for at least another hour before cutting up and serving.