Preheat the oven to 200°C (180°C fan)

Line a baking tray with baking paper.

Chop the pistachios in a food processor.

Place in a bowl with the sugar and mix well.

In a separate small bowl, beat the egg.

Trim the rhubarb and cut each stalk into 20cm lengths.

Unroll the pastry and lay it out on a work surface.

Trim the pastry to a square.

Using the tip of a knife, but making sure not to cut at the way through, make an incision all the way around the square about 2.5cm in from the outside edge.

Cut four 22.5 x 2.5cm strips out of the remaining pastry.

Add the four extra sheets to the square, so that it "frames" the tart.

Brush the pastry with the beaten egg.

Prick the base all over with a fork then scatter three-quarters of the pistachio mixture evenly over the base.

Bake for 15 minutes.

Then remove from the oven and arrange the rhubarb as tightly and neatly as possible in a row inside the frame.

Scatter the remaining pistachio sugar haphazardly over the rhubarb.

Bake until the pastry is golden.

Fantabulous with some whipped cream.