We have tons of meats and vegetables now. Some might say we could use more meats but it's high time we started throwing shit in a cauldron and boiling it all together. You could even make a fun minigame out of naming recipes based on who eats a certain recipe.
It would essentially be processing foods into a multiFEP format for the trade off of a higher FEP:hunger ratio. Ingredients need simply be used on a cauldron and so many ingredients should require more water in the cauldron. All ingredients added should have a fixed liquid value across the board.
Quality of the water should stay out of the main formula. It should multiply its quality modifier by the diversity FEP reduction inherent to the recipe. High quality water as such will have value but not cause the base FEP value of the ingredients be diminished in any way. Soup's diversity FEP should be unique bowl:bar but only for a given recipie and not interfere with the diversity FEPs other foods provides (even if they were ingredients).
Soups would require minimal additional tilesets and the dynamic crafting sadly stays outside of the current crafting system (but remains far easier to implement than a new crafting system).
As a tangent it would be nice to see some basic cooking and seasoning herbs start being foragable and/or farmable. Adding these herbs can have varying effects on the formula for soup creation and could have different effects in different combinations.