The best madeleines I've had were from the Dominique Ansel Bakery in New York, where they're baked to order and served warm. Fortunately for us, the madeleine recipe is featured in the pastry chef's cookbook Dominique Ansel: The Secret Recipes. This version is adapted for a green tea flavour, and while Ansel flavours the madeleines with grated lemon and orange zests, I've left them out so they don't overwhelm the matcha (green tea powder). For the same reason, be sure to use a light, subtle-tasting honey.
Matcha - green tea powder - comes in different "grades". The type labelled for cooking or baking is a low grade - it's pale in colour and isn't very fresh. There's no need to buy tea-ceremony quality matcha - which is very expensive, and its subtleties would be lost when baked, anyway. But buy good-quality drinking matcha, which will have a vibrant green colour. Buy as small a pack as possible, and store it in an airtight container. What you don't use for this recipe can be whisked and drunk as green tea.
Make the batter the day before you want to use it, and let it rest in the fridge. This recipe makes about 100 small, bite-size madeleines, but there's no need to bake them all at once. Keep the batter in the fridge for up to a week and bake the madeleines as needed; they should be eaten fresh and warm.
Put the butter in a small saucepan and place it over a medium flame. When the butter is melted and sizzling, stir in the honey, then cool until tepid.
Put the flour, sugar and salt in a large bowl. Use a small sieve to sift the matcha and baking powder directly into the bowl holding the other ingredients. Use a whisk to stir the ingredients until they are evenly combined.
Whisk the eggs, then add them to the dry ingredients. Whisk until thick and smooth. Add the butter and honey and whisk until fully incorporated. Scrape the mixture into a container, cover with the lid then refrigerate for at least eight hours.
Preheat the oven to 190°C (375°F), or 180°C (350°F) if it's a convection oven. Spray a mini-madeleine pan with pan coating. Put the batter into a piping bag fitted with a 6mm (¼in) plain tip. Pipe the mixture into the moulds so they are three-quarters full (or use a small spoon to fill the moulds). Bake the madeleines for five to six minutes, or until they are cooked: they will be fragrant, firm to the touch and matte on the surface. As soon as you take them out of the oven, bang the pan on the work surface to loosen the madeleines so they fall out of the moulds. Turn them so the fluted side is up, dust them very lightly with icing sugar, then serve them immediately.
If you're baking more madeleines immediately, clean the mould then dry it and spray it before using it again.