Dissolve the instant coffee in boiling water and leave aside to cool.
Coarsely chop the macadamia nuts and set aside. Mix the coca, rice flour and baking powder together in a mixing bowl and set aside.
Using an electric mixer, cream the butter and sugar together at a medium to high speed until pale and fluffy. Slowly add the beaten eggs while continuing to mix the butter and sugar.
Once the eggs are combined into the butter and sugar mix, add the flour and coca mix in two halves. Mixing on a slow speed the whole time. Finally add your instant coffee while mixing on a high speed.
Using a rubber spatula mix in the macadamia nuts in by hand.
Spoon into muffin cases and bake for 30minutes.