Even though they're technically little cakes, these perfectly spongy matcha green tea madeleines would be a delightful addition to your holiday cookie tray. For the coveted bump, an overnight rest of the batter in the refrigerator is best.
Sift together the flour and baking powder into a bowl and set aside.
In another bowl, combine the eggs and sugar and sift in the matcha powder. Using a whisk, beat the mixture until well blended--you want as little matcha clumps as possible. Squish the butter through your fingers (or mash around with a rubber spatula) before adding to the egg mixture. Beat in the butter with a whisk until evenly distributed. This will take about 2 minutes and you might end up with very small clumps of butter and this is okay. Whisk in the flour/baking powder until they have been incorporated and the mixture is smooth. Scrape the sides of the bowl and smooth the batter. Press a piece of plastic wrap against the surface of the batter and chill overnight. If you can't wait, you can chill for one to three hours but your bumps won't be as pronounced.
When you are ready to bake the madeleines preheat your oven to 425ºF. Butter a 12-mold madeleine pan then dust it with flour (even if you are using a nonstick pan), tapping out the excess.
Spoon the batter onto the molds--you don't have to worry about spreading the batter to cover the molds, the heat will do this. Place the pan in the oven and immediately reduce the heat to 350ºF. Bake the cookies for 13 minutes or until the cakes are domed and spring back when pressed gently. Check at the 11-minute mark. Unmold the cookies and cool them for a few minutes before serving. These will keep for a few days in an airtight container.