1.Beat butter, rind, sugar and egg in small bowl with electric mixer until combined. Stir in sifted flour and milk in 2 batches.
2.Heat un-greased gem irons in hot oven for 5 minutes just before use; grease with cooking oil spray.
3.Drop tablespoons of mixture into prepared gem irons, sprinkle with nuts. Bake in oven 190°C for about 12 minutes.
4.Meanwhile, make lime syrup; combine all ingredients in small pan, stir over heat, without boiling, until sugar is dissolved. Simmer, uncovered, without stirring, 2 minutes.
5.Turn pistachio lime gems onto wire rack, brush all over with hot lime syrup.
Old-fashioned cast gem irons are available from specialty cookware shops or second-hand shops.Note