175g unsalted butter, chopped, at room temperature
2 tablespoons caster sugar
2 x 85g packets raspberry or lime jelly crystals
1 cup self-raising flour
1 cup plain flour
½ x 330g packet royal icing (1 ¼ cups)
1 ½ - 2 tablespoons hot water
Grease and line two large oven trays with baking paper.
Place butter, sugar and 1/2 cup of the jelly crystals in a small bowl of electric mixer, reserving remaining jelly crystals for decoration.
Beat until light and fluffy. Add egg. Beat until combined. Transfer to a large bowl. Add flours. Stir until combined. Roll level tablespoons of mixture into balls. Place, about 4cm apart, on prepared trays.
Cook in a moderately slow oven (160C), swapping trays halfway through, for about 12 minutes, or until just firm to touch. Remove. Stand on trays for 5 minutes. Transfer to a wire rack to cool completely.
To make icing, place icing mix in a medium bowl. Stir in enough hot water (we used about 1 ¾ tablespoons) to form a spreadable consistency. (Icing should just drip down sides of biscuit, without being too runny.)
Spoon 1 teaspoon of icing over each biscuit. Spread slightly. Sprinkle with some of the reserved jelly crystals. Allow icing to set before serving.