Pastry: Beat butter, icing sugar and orange rind in an electric mixer until pale and fluffy (4-5 minutes), add yolks and beat to combine. Add remaining ingredients and mix until just combined. Form into a disc, wrap in plastic wrap and refrigerate until firm (2 hours).
Roll two-thirds of hazelnut pastry to 3mm-thick on a lightly floured piece of baking paper and line a 24cm-diameter tart tin. Trim edges and refrigerate until firm (30 minutes). Roll out remaining dough on a lightly floured piece of baking paper to a rough 24cm-long rectangle, place on an oven tray and refrigerate until firm (30 minutes).
Preheat oven to 180C. Combine strawberries, sugar, cornflour, rinds and vanilla seeds in a bowl and fill pastry case.
Cut remaining pastry lengthways into 12mm-thick strips and form a lattice pattern over strawberry mixture, trimming overhanging ends. Brush pastry with eggwash, bake until crisp and golden (30-35 minutes), cool in tin for 30 minutes then remove and cool to room temperature. Dust liberally with icing sugar before serving.