Matcha powder
Finely ground Japanese green tea, bright green, with a grassy, slightly bitter and faintly sweet taste.
Matcha is now sold in many supermarkets, drugstores and health food shops, but better quality is easier to find in Asian grocers, tea shops or by mail order; for baking and cooking the cheaper culinary grade is enough, though it is more bitter and less vivid in colour. There is no equivalent substitute, because colour, flavour and the fine powder together define it.
Substitute:
No good substitute: finely ground sencha or other green tea gives some of the bitterness, but neither the vivid colour nor the fine, smooth texture, and it tastes flatter and often more bitter.