• Preheat the oven to 170°C fan / 190°C and prepare a large baking tray by lining it with non-stick baking paper.
• In a large mixing bowl, cream together the softened butter and caster sugar until light and well combined. I use an electric hand whisk.
• Add the milk and vanilla extract, then mix again.
• Add the gluten-free plain flour and xanthan gum. Mix until all of the flour is incorporated and the dough begins to come together. If it still seems too dry to form a workable dough, add up to 1 tsp extra milk.
  
• Lightly flour a large sheet of non-stick baking paper and the rolling pin, then roll the dough out to around 6mm thick.
  
• Use a 2cm round cutter (or the wide end of a piping nozzle) to cut out as many little biscuits as possible. Re-roll the scraps and continue cutting until all of the dough is used.
  
• Transfer the biscuits to the prepared baking tray, ideally using a small palette knife.
  
• Place into the preheated oven for around 8-10 minutes, until set and only very slightly golden around the edges. Keep a close eye on them as their small size means they can colour quickly.
• Allow the biscuits to cool briefly on the tray before transferring them to a cooling rack to cool completely.
  

Make the royal icing

• Add the egg white and icing sugar to the bowl of a stand mixer fitted with the whisk attachment. Alternatively, an electric hand whisk and a (clean) large mixing bowl is fine too.
• Starting on a low speed, mix for around 5 minutes until thick, smooth and roughly toothpaste-like in consistency.
  
• If the royal icing feels very stiff, mix in ¼ tsp water at a time before transferring it to the piping bag, until it still holds a firm peak.
• Divide the icing equally between three small bowls.
• Leave the first portion white and mix in ¼ tsp vanilla extract.
• Colour the second portion pale pink using a drop of pink food colouring gel. Add 1 drop raspberry flavouring, mix thoroughly and taste. Add a second drop if a stronger raspberry flavour is wanted.
• Colour the third portion pale purple using a drop of purple food colouring gel. Add 1 drop blackcurrant flavouring, mix thoroughly and taste. Add a second drop if needed. Keep the flavourings restrained as they’re high-strength.
  

Pipe the Iced Gems

• Prepare the three piping bags with an open-star nozzle.
• Fill the piping bags with each icing. Working with one colour at a time, pipe a small ridged peak directly into the centre of each completely cooled biscuit. I like to gently twist the piping bag as I do it. When piping, allow the base of the icing to make contact with the biscuit, stop squeezing, then lift the nozzle straight upwards. Repeat with the other two colours.
  

Dry the icing

• Reduce the oven temperature to 70°C fan / 90°C.
• Arrange the finished Iced Gems on a baking tray lined with non-stick baking paper and place them into the oven for 45–60 minutes, until the royal icing is completely hard and crisp.
• Allow the Iced Gems to cool completely before transferring them to an airtight container.