Genshin Impact has some complicated daily commissions, and one, in particular, gives a tricky hidden achievement that you can get if you follow the correct steps. Note, as these are daily commissions, obtaining the commission, to begin with, takes a bit of luck.
The daily commission in question is one given by Tang Wen. In this commission, Tang Wen is feeling homesick and desires food back in her homeland in Liyue. She’ll ask you to make a dish for her, which can range from a variety of different foods based on her moods. (I got a version featuring fish: the Black-Back Perch Stew, Squirrel Fish, or Mondstadt Grilled Fish.)
Paimon will ask you which snack you want to feed Tang Wen, but no matter what decision you make, you can feed her any one of them. Go to cook the snack you want, but here’s the trick: you must cook the food manually and mess up on purpose. This creates a “suspicious” version of the dish that you can bring back and feed Tang Wen. You’re essentially giving her food poisoning. (You SHOULD be able to make a suspicious version of any dish and trigger the secret commission.)
A number of days later, you’ll get another commission from Tang Wen. She’s not happy, as the food you cooked made her feel sick. This time, Tang Wen needs food to trigger her appetite again and will ask you to make Jueyan Guoba, Bamboo Shoot Soup, or Grilled Tiger Fish.
Make a perfect version of the dish, bring it back to Tang Wen, and you’ll receive the “Liyue Ichiban” special achievement! You’ll get the usual 10 Primogems for completing the daily commission and another 5 Primogems from the new achievement.