There is a scroll-shaped thing tied with a red ribbon in the upper left corner of Happiness Kitchen, which is the "Chef Certificate Task". Click inside and you can do the task. Tasks are unlocked by series, and the menu limit you have for each task will increase by two.

The tasks are: breaking eggs, cutting cucumbers, peeling potatoes, side dishes, kneading dough, making jiaozi, putting peas, baking sausages and making biscuits. There are tutorials to watch.