Rub oil around the inside of two baking trays or insert a cake liner. Preheat the oven to 180°C, Fan 160°C, 350°F, Gas 4.
Measure the flour, mixed spice, xanthan gum and soda into a large bowl and stir to combine.
Put the sugar, butter and syrup into a saucepan and heat gently, stirring occasionally until dissolved. Pour the mixture into the prepared flour and mix lightly.
Grate the lemon rind into the bowl and stir again. Add the egg yolk and stir to gather together a soft dough.
Lightly dust the work surface and rolling pin. Roll out the dough to the thickness of 2 x £1 coins.
Press the bunny cookie cutter into the dough and transfer the cut shapes to the prepared baking trays.
Gather the left-over dough into a ball, roll it out again and cut more shapes.
Bake for 18-20 minutes. Leave to cool on the tray.
Sieve the icing sugar into a bowl, add the lemon juice and stir until a syrup forms.
Spread the icing over the cold bunny-shaped biscuits and leave until set.
When the icing has set, decorate the biscuits with coloured icing.