Preheat the oven to 150°C/300°F/gas mark 2. Spread the rhubarb out in a single layer in a large roasting tin. Sprinkle over the sugar, cardamom and orange zest. Pour over the juice.
Cover the tin with foil and roast for up to an hour, until tender. Strain out the juice and pour into a saucepan. Bring the juice to the boil, reduce the heat and simmer until it has thickened and reduced by half. Allow to cool.
Meanwhile, mix together the ground almonds, sugar and cream to a smooth paste in a mixing bowl and set aside. Increase the oven temperature to 180°C/350°F/gas mark 4.
Cut the puff pastry into six equal-sized squares. Place on a large baking tray lined with baking parchment. Using a sharp knife, create a rim on each square by scoring a line about 1cm away from each edge, without cutting through the pastry. Spread the almond paste over the pastry, not covering the rim. Brush the rim with beaten egg and place in the oven. Bake for 10–12 minutes.
Cut the rhubarb into strips and place on the tarts. Drizzle with some of the rhubarb syrup and sprinkle with the toasted nuts. Dust with icing sugar. Serve the rest of the syrup on the side with a generous dollop of clotted cream.
Recipe courtesy of Reza’s Indian Spice by Reza Mahammad, published by Quadrille (£17.99, hardback). Photos © Martin Poole.