I am pretty sure that cooking experience can only be gained through working in a cooking job. The food channel and the food book increase skill (Basic Cooking, I think) but not cooking experience. My character has given plenty of dinner parties, but I’ve never seen that make a difference.
My character is now at pay grade 6 (max) as a Sous Chef, and the job description in the Career Details screen still does not show cooking experience gain as an effect. Every better job requires 100% cooking experience. It’s frustrating not knowing what the next step is and grasping at straws. Does she have to wait for a special event? Did she miss some experience by skipping over a job on her way up the career ladder? Does she have to increase her IQ to be able to learn the final 5%? The possibilities are endless, but I don’t want to spend hours going down blind alleys.