STEP 1 Preheat oven to 170ºC. Beat butter and caster sugar in the bowl of an electric mixer on high speed for 5 minutes until light and creamy. Beat in egg, yolk and orange zest, then gently fold in flour until dough comes together.
STEP 2 Line 4 oven trays with baking paper. Roll out dough using 2 strips of 6mm-thick plywood as guide rails. Using an 8cm round cutter, cut out 24 discs. Arrange discs on prepared trays. Freeze for 5 minutes. Bake for 12-15 minutes or until lightly golden.
STEP 3 Put jam in a small pan and cook over a low heat until just boiling. Put marshmallows and lemonade in a separate pan over a low heat. Cook, whisking constantly, for 5 minutes or until marshmallows melt and thicken.
STEP 4 Brush biscuits with jam, then sandwich pairs together with a generous spoonful of marshmallow. Set aside to cool. Dip biscuits into chocolate to coat completely. Cool thoroughly. Serve.