1. Preheat the oven to 325° Fahrenheit. With an electric hand mixer, beat the egg whites in a large bowl with salt and cream of tartar until they are risen. Now beat in the sugar, a couple of tablespoons at a time, sprinkling it over the egg whites and beating about 20 seconds with each addition. Fold the sifted flour into the meringue in three stages, and then stir in the tonic water.
2. Arrange muffin paper baking cups inside a muffin tin and fill two thirds full. Bake for 15-20 minutes until lightly golden on the surface and still springy to the touch. Remove and let cool.
3. Spoon mascarpone into a bowl and beat in the gin and then the syrup and tint it the palest green with a little food coloring. Fill a icing bag or ziploc with the tip cut off to frost the cupcakes.
4. Use a decorative toothpick to spear lime slices in sugar or jellied candies and insert one into each cupcake.

Makes 12 cupcakes.