Use 2 baking trays. Preheat the oven to 160°C; line baking tray with baking paper.
Beat egg whites with electric beaters until very stiff. Add half the sugar, a little at a time, beating until mixture is shiny and the sugar has dissolved.
Using a large whisk, fold in the remaining sugar, the ground nuts, chocolate, sultanas, zest, rum, cinnamon and flour, taking care that the beaten egg whites retain their shape and stiffness. Using a teaspoon, shape 30 walnut-sized mounds of mixture and place on baking trays.
Cook for 12–15 minutes (the low temperature will dry the macaroons out rather than actually bake them); when done, the insides should still be soft. Transfer to a wire rack.
Combine the icing sugar and lemon juice in a small bowl. Cover macaroons thinly with icing while still hot; decorate each one with half a glacé cherry.