Rhubarb, orange and pistachio pie

My partner, Simon, fancies himself a bit of a rhubarb connoisseur. His family home in New Zealand has the most incredible kitchen garden which is constantly overflowing with whatever is in season. In the spring, there is rhubarb. There’s always pressure when it comes to him trying one of my rhubarb desserts but he ate his whole piece of this pie in silence and then went back for more. So it must be good, then.