For the macarons, mix the almonds and icing sugar and sieve. Add one egg white and mix until smooth. Soak the sugar in water for 5 minutes. Add the egg white powder to the remaining egg white
Heat the sugar water to dissolve the sugar and bring to a boil. Use a thermometer and keep boiling until the syrup reaches 112°C
Whisk the egg whites, and after 30 seconds add the sugar syrup and food colouring and keep whisking to a meringue. Whisk for a further 30 seconds then reduce the speed to medium and whisk until cool
Fold the meringue into the paste, trying not to lose any air. Spoon into a piping bag. Pipe drops 2.5cm in diameter onto a baking sheet lined with baking parchment, and leave for 30 minutes to air dry
Heat the oven to 160°C/Gas mark 2. Bake for 14 minutes, checking to make sure they are not browning too much. They should be a light gold. Cool and store in an airtight container
For the passion fruit filling, whisk the eggs, purée, caster sugar and butter together in a bain-marie until thick and creamy
Blitz in a blender with the xanthan gum, then pass through a fine sieve and chill. Spoon into a piping bag. Sandwich two macaroons together with filling
Serve in a bowl, dusting with icing sugar if you so wish
