Wash the rhubarb and cut the stems into 2.5cm-3cm pieces. Add the sugar and vanilla extract and mix.
Place the pieces in an ovenproof frying pan of about 24cm diameter and cook over low to medium heat for 6-8 minutes maximum. Do not overcook — you want
softened but visible pieces of rhubarb.
Add the cranberries then leave to cool before arranging the pieces in the pan — this will be the top of the tart.
On a lightly floured surface roll the pastry to 3mm thickness and cut a circle the same diameter as the pan — use a plate of the same size as a guide. Sprinkle with a little flour.
Roll the pastry around a rolling pin so you can lift it up. Then unroll it over the cooked rhubarb in the pan.
Gently prick the pastry all over lightly with a fork.
Cook at 180°C for 30-40 minutes until golden brown and crisp.
Carefully remove from the oven – making sure to remember to use an oven glove around the pan handle — and turn the tarte over on a serving plate