Sui Mi Ya Cai (碎米芽菜) is a type of preserved mustard green from Sichuan, China. After a process of fermentation, the result is a sweet, tangy, and slightly salty flavor unique to Sui Mi Ya Cai. This unique flavor makes it an essential ingredient to dan dan noodles and is hard to reproduce using other ingredients. You can find Sui Mi Ya Cai is usually sold in vacuum-sealed packets in Chinese or Asian grocery stores.