For the frosting: In a heatproof bowl whisk together water, tea, sugar, egg whites, cream of tartar and salt. Ensure the tea is dissolved. Put the bowl over a saucepan of simmering water; beat constantly, preferably with an electric whisk, until the mixture holds stiff peaks. This takes between 5 and 7 minutes. Remove from the heat and transfer the frosting to a cool bowl. Beat until the frosting is cooled, about 2 minutes.
To assemble: Prick each cake with a skewer. Spoon over the syrup. Swirl over the match tea frosting. Serve with green tea.