Each new dish, ie. each new recipe that is a masterpiece, should give you a gastronomy point. You can only get one point off a single recipe, although it is possible to get multiple masterpieces by changing the recipe a little. Testing should be done to determine if it is possible to codify masterpieces and make gastronomy more understood and easier to produce.
After consuming a masterpiece, the next leek you grow will give an additional seed. Eating a masterpiece that does not give gastro still results in the additional seed
With a Gastronomy skill of 7 or higher, you gain a menu option to “critically evaluate meal”, which is required to calculate the potency of an ingredient. See the Cooking Guide for details.
Also worth noting, you gain one permanent perception point at 7, 43 and 243 gastronomy levels.