1.Preheat oven to moderate, 180°C. Lightly grease and line 4 oven trays with baking paper.
2.In a small bowl, using an electric mixer, beat butter and sugar together until light and creamy. Add egg yolk, beating well to combine.
3.Sift flour and soda together. Fold into creamed mixture with honey, mixing well. Cover and chill, 30 minutes.
4.Knead mixture gently on a lightly floured surface. Roll out between 2 sheets of baking paper until 5mm thick.
5.Using a 4.5cm cutter, cut rounds from dough. Arrange on prepared trays. Bake, 10-12 minutes, until firm to touch. Allow to cool on trays.
6.Meanwhile, prepare filling by beating egg white with a wooden spoon until frothy. Add icing sugar one spoonful at a time, beating well after each addition. Add butter, stirring until combined. Spoon half the icing into a small bowl and add a few drops of pink colouring. Mix well.
7.Make sandwiches with the biscuits, with the icing in the middle, half the biscuits with pink icing and half with plain white. Set aside until filling is firm.