For vanilla pastry, process flour, icing sugar and a pinch of salt in a food processor to combine, add butter and vanilla seeds and pulse until mixture resembles fine crumbs. Add egg and yolk, pulse until mixture just comes together, turn onto a lightly floured surface and form into a disc. Wrap in plastic wrap and refrigerate to rest (2 hours).
Meanwhile, melt butter in a large saucepan over medium-high heat, add apple and stir occasionally until edges begin to soften (3-4 minutes). Add rhubarb, sugar, cinnamon, vanilla bean and vanilla seeds and stir occasionally until beginning to soften (6-8 minutes). Stir in citrus juices and rinds and strain through a sieve (reserve liquid separately; discard vanilla bean and cinnamon quills). Spread on a tray, cool to room temperature, stir in breadcrumbs, set aside.
Simmer reserved rhubarb liquid in a small saucepan until reduced to a thin syrup (10-15 minutes), set aside.
Preheat oven to 180C. Roll two-thirds of the pastry on a lightly floured surface to 3mm thick, line a 23cm-diameter, 4cm-deep pie tin, trim edges, refrigerate to rest (30 minutes).
Meanwhile, roll out remaining pastry on a lightly floured surface to a 3mm-thick round, cut a 1.5cm round from centre (discard), place on a tray and refrigerate until required.
Spoon rhubarb mixture into tart case, piling high in the centre, brush edges of pastry with eggwash and place pastry round on top, pressing edges with a fork to seal. Brush top with eggwash, scatter with combined demerara sugar and cinnamon, bake until dark golden (45 minutes-1 hour; cover edges with foil if necessary to prevent burning) and stand in tin to rest (20 minutes).
Meanwhile, for cinnamon custard, bring cream, wine and cinnamon to the simmer in a saucepan over medium heat, remove from heat and stand to infuse (5 minutes). Whisk yolks and sugar in a bowl until thick and pale, add cream mixture, whisk to combine. Return to pan, stir over medium heat until mixture coats the back of a wooden spoon thickly (4-5 minutes). Strain and serve warm with warm rhubarb and apple pie and rhubarb syrup.