Place flour and icing sugar in a food processor and whiz to combine. Add the butter and whiz until the mix resembles fine breadcrumbs, then add the vanilla and egg and whiz until a dough forms. Turn onto a clean surface and gently knead to bring together. Divide dough in half and shape into rectangles, then wrap in plastic wrap and chill for 1 hour until firm.
Preheat oven to 180°C. Line 2 large baking trays with baking paper. Roll out each pastry rectangle between two sheets of lightly floured baking paper until roughly 22cm x 32cm. Use a ruler to cut each piece in half, trimming the excess, so you have four 10cm x 30cm rectangles. If the pastry is too soft to cut, chill until firm.
Place pastry on prepared trays and prick all over with a fork. Bake for 10-12 minutes, swapping trays halfway, until lightly golden brown. Remove from the oven and cool.
To make the icing, place icing sugar and 1½-2 tbs boiling water in a small bowl and mix to combine. The mixture should be thick and not too runny. Stir through half the crushed freeze-dried raspberries.
For the filling, place fresh raspberries in a small bowl and roughly crush with a fork. Add the jam and orange zest and mix to combine. Set aside.
To assemble, spread raspberry filling over two of the pastry pieces, top each with a plain pastry piece, spread over the icing and sprinkle with remaining freeze dried raspberries. Carefully cut each into 6 bars to serve. (This is best assembled just before serving.)
