Melt the butter gently in a small pan then set aside to cool.
Whisk the eggs and sugar together until the mixture is pale, thick and has trebled in volume. You can do this by hand, but electric beaters make the job a lot easier and faster.
Pour the butter in down one side of the bowl and fold this in as gently as possible together with the lemon zest.
Sift in the flour, discarding any bits of bran left in the sieve. Then sift in the matcha and baking powder. Fold in as gently as possible trying not to lose too much air from the eggs.
Place 1 tbsp of the mixture into each of 16 Madeleine moulds. I use silicone, but if using tin ones, you'll need to butter and flour them first.
Bake in a pre-heated oven for 10 minutes at 200℃ (400℉, Gas 6) or until well risen and firm to the touch. Turn out onto a wire rack to cool, then dust with caster sugar if desired.
Traditional madeleine recipes state that the batter needs to rest for at least 30 minutes prior to going in the oven. I don't always have time to do this and I haven't really noticed much difference. But if you have the time, do cover the bowl and leave it for a while. Then spoon the batter into the moulds just before baking.If you only have a 12 hole madeleine tin, its fine to bake the madeleines in two batches. See above note re resting.Best eaten on the day of baking and preferably soon after emerging from the oven.Please note: calories and other nutritional information are per serving. They're approximate and will depend on serving size and exact ingredients used.