Preheat the oven to 180C/170C Fan/Gas 4. Grease two baking trays and line with parchment.
Put the butter, orange zest and orange blossom water in a free-standing mixer and mix until soft. Add the sugar and beat until light and fluffy. Add the flour and bring the mixture together with your hands.
Generously flour a work surface and roll the dough to 5mm/¼in thick. Use a cutter to cut out 48 star shapes. Use a palette knife to transfer the shortbread to the prepared baking trays. Prick each star with a fork and place in the fridge for 15 minutes.
Bake for 15 minutes, or until golden brown. Leave to cool on the tray for 5 minutes before transferring to a wire rack.
For the marshmallow filling, put the sugar, liquid glucose, salt and 2½ tablespoons water in a small, heavy bottomed saucepan. Place over a high heat and stir until all the sugar has dissolved. Use a sugar thermometer to monitor the temperature, once it has reached 115C remove from the heat (CAUTION: boiling sugar is extremely hot. Handle very carefully).
Whisk the egg whites and vanilla bean paste in a free-standing mixer until they form soft peaks. With the whisk going, add 2 tablespoons of the sugar syrup. Gradually add the rest of the syrup and continue to beat for about 5 minutes, or until a stiff consistency is achieved. Pour into a piping bag and place in the fridge.
Melt the chocolate in a glass bowl over a pan of simmering water, making sure the bowl doesn't touch the water, then set aside to cool.
To assemble, pipe the marshmallow into the middle of a shortbread and use a blowtorch to brown. Gently place another shortbread on top to make a sandwich. Repeat this process with the remaining shortbread and marshmallow to make 24 sandwiches.
Using a fork, drizzle chocolate over each sandwich in lines. Leave to cool.