Prepare the the cupcakes: Preheat the oven to 180°C. Fill a 12-hole muffin tin with paper cupcake cases.
Cream the butter and sugar together in a bowl until pale: Beat in 2 eggs a little at a time. Fold in the flour using a large metal spoon or spatula, adding a little milk until the mixture is of a dropping consistency. Half-fill each of the paper cases.
Bake the cupcakes: Bake in the oven for 15 minutes, or until golden-brown and well-risen. Cool on a wire rack.
Prepare the frosting: In a heatproof bowl whisk together 50ml water, 1 tbsp fine matcha powder, 150g sugar, 2 egg whites, 1/2 tsp cream of tartar and 1 pinch 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.
Prepare the yuzu syrup: Combine 30ml water and 30g sugar in a small pan over a low heat. Allow the sugar to dissolve. Add 30ml yuzu juice to your taste. Allow the syrup to cool.
Assemble the cupcakes: Prick each cake with a skewer. Spoon over the syrup. Swirl over the match tea frosting. Serve with green tea.
