Aqua faba is the water you’ll find in a can of chickpeas. It makes a good alternative to egg white in order to make vegan meringue.
Heat the oven to 80°C/180°F/Gas ¼ (don’t use the fan oven).
Put the aqua faba and xanthan gum in the bowl of a stand mixer fitted with the whisk. Whisk the mixture on high speed until it forms stiff peaks.
With the whisk still running, gradually add the caster sugar, one spoonful at a time, whisking until the mixture is thick and glossy. Add the lemon juice and cornflour and whisk again to combine.
Divide the mixture equally between 2 bowls. Add the rose water and pink food colouring to one bowl. Stir to combine. Add green food colouring to the other bowl. Stir to combine.
Spoon each coloured meringue into its own piping bag and snip the ends to make a 1cm hole in each bag.
Pipe 20 meringue kisses of each colour onto the lined baking sheets, then sprinkle the pink meringues with rose petals and the green with pistachios.
Bake for 1½–2 hours until firm. Remove from the oven and leave to cool, then serve immediately.