Thawed the frozen shortcrust pastry. Trimmed and cut into 4cm lengths the rhubarb. Juice the large oranges. Toast the flaked almonds.
- 1 On a floured surface, roll out the pastry to the thickness of a pound coin. Use it to line a 20cm tart tin, leaving 2cm pastry hanging over the edge. Prick the base with a fork and chill in the fridge for 30 minutes.
- 2 Heat the oven to 200°C/180°C fan/gas 6. Line the pastry case with greaseproof paper and fill with baking beans. Bake for 20 minutes, then remove the beans and paper.
- 3 Trim the excess pastry with a sharp knife. Bake for a further 5-10 minutes, until the pastry is golden and crisp. Set aside to cool.
- 4 Meanwhile, put the rhubarb in a single layer on an oven tray. Scatter over 3 tbsp sugar. Pour over the orange juice and bake for 15-20 minutes. Set aside to cool.
- 5 Beat the mascarpone with ¼ teaspoon of vanilla extract and remaining sugar until smooth. Whip the cream until it stands in soft folds, then stir into the mascarpone.
- 6 Spoon into the cooled pastry case, top with the rhubarb and scatter over the almonds.