It's been a while since I was chasing that score, but I think that after cooking the same recipe 10 times, quality of meal is improoved by one level (from nice to very nice, from very nice to great etc). There is a counter in journal skill (total number of meals) as well as the "basic quality" level of the meal - all recipes unlocked on low levels start with normal quality, including hot dogs. It's a loot of cooking but eventually you'll get there.