Preheat the oven to 180°C (350°F/Gas 4) and grease six 125 ml(4 fl oz/½ cup) pudding pots. Put the rosehips and tea bags in a saucepan with 1.5 litres(52 fl oz/6 cups) of water and bring to the boil. Simmer over low heat for 20 minutes or so, until you have a good rich colour and flavour. Leave to cool for a while.
Meanwhile, spread the pistachios on a tray and toss with ½ teaspoon of the sugar. Roast in the oven for about 5–10 minutes until they are crisp, then let them cool before roughly chopping them.
Strain the rosehip liquid into a bowl and throw away the solids. You should have about 750 ml(26 fl oz/3 cups) of liquid. Put 250 ml(9 fl oz/1 cup) of it in a heavy-based saucepan over medium heat. Just before it comes to the boil, add the semolina in a fine steady stream, whisking constantly so that no lumps form. As it starts to thicken, stir in the milk, vanilla and 115 g(4 oz/½ cup) of the sugar. Lower the heat and simmer for about 10 minutes, whisking almost continuously, until thickened and smooth. Take the pan off the heat and stir in the butter. Sit the pan in a sink of cold water, stirring a few times to help it cool. Whisk in the egg.
Meanwhile, put 375 ml(13 fl oz/1½ cups) of the cooking liquid and the remaining sugar in a small saucepan and bring to the boil, stirring until the sugar has dissolved. Lower the heat and simmer for 15–20 minutes, stirring occasionally, until the syrup has thickened. Keep on one side.
Divide the semolina among the pudding pots (they won’t be completely full). Cover each one with a circle of baking paper and put the pots in a roasting tin. Pour hot water into the tin to come halfway up the sides of the pots. Carefully move the tin to the oven and bake for about 30 minutes, until the puddings are puffed, set and slightly pulling away from the sides of the pots. Remove from the oven and the water bath and leave to cool a little (they will lose a bit of their height). Peel off the baking paper and unmould them onto serving plates. Drizzle with the syrup and scatter some pistachios on top. Serve warm or at room temperature.