Once the part-baked pie case & your rhubarb filling has cooled down, you can now add the cooked rhubarb. To make the pastry twist top, take one long strip of the pastry just cut, use both hands & twist from one end to the other.
Then on some paper, make a spiral for your starting point - like a rose. See video for reference. Alternatively, you can skip the initial twist, & twist the pastry while you are forming a spiral. (See Photo 16 & 17 below). Just be careful not to let the pastry break. Chilling the pastry before construction actually can make the pastry too hard and break more easily. So if too soft or your hands are too warm, just chill for 5 minutes at a time.
Using the left-over egg-wash, brush all over this pastry spiral before carefully transferring to the centre of the pie, on top of the rhubarb filling. Then take a second pastry strip and twist from both ends, before joining onto where the first pastry spiral ends. See Photo 17 below. Having egg-wash on the sides of the pastry helps them join. Repeat with more long strips of pastry till you have filled the top of the pie. (See videos, and Photo 18 below for reference). If the pastry twist is not quite centre, gently and carefully shake the pie dish till it lines up better.
Gently brush egg-wash on top of all the pastry, including the crust edge, before baking for about 14-18 minutes. Turn the dish during baking if needed & check after 12 minutes until you get an even golden colour, not pale (If the pie case edges are colouring too much, you can cover using foil - just cut out a circle in the centre, to allow the pastry in the centre to develop its colour). Place on a cooling rack to cool down before attempting to remove from the pie dish. (If you baked on top of a baking tray/sheet, remove this and just place the pie dish on the cooling rack). See Photo 18 below.
Removing from a loose-bottomed pie dish - simply place the pie on top of a jar for example, & pull the ring of the tin down. It’s easy just to cut the pie on the tin’s loose base. Alternatively use a cake lifter or push the pie onto a flat plate (just make sure the pie is not still hot).