+1
There is nothing that tells us how the cooking works.
Like, if I have 5 starch, will I use up everything in one cooking, or only 1?
What if I have 5 starch and 1 steak? Will I use up all six, or just 1 of each?
And will specific ingredients be optimal with other specific ingredients, or does mixing stuff not matter?

Each ingredient is worth a certain "percentage". 100% = one meal. The game shows you the total "percentage" of ingredients when you add them to the food workshop.

For example, one starch = 60% and one potato = 20%. You can make a meal by combining a starch and two potatoes in the cooking pot (60 + 20 + 20 = 100%).

You should try to be as efficient as possible when combining ingredients (e.g. if you cook a meal worth 150%, the extra 50% is wasted; you should either try to go up to 200% and cook two meals, or stick closer to 100% with no excess).

Also, upgrading the food workshop makes the meals better. A meal cooked at a level 1 workshop gives you +30 hunger, while the same meal cooked at a level 2 workshop gives you +40 hunger, etc. The specific ingredients you use does not change how much hunger a meal gives you.

came here for recipies
milk starch and crackers make bread got any more?

There is one for hamburger I think. Don't exactly know it.

For food I have the rule: If the hunger it restores is higher than 30/% or 40/%(don't have kitchen lvl 3), then I eat it so. Some items can be cooked so(fresh meat/fish) that doubles their hunger stat I think, so keeping this in mind is also a thing. In nation park and campsite are additional ones, that produce different food items(though what they take as itemamount and what they give is bad so only for purpose of itemdiscovery). And when your fresh meat rot, at least bait is something you can make out of it! - or you use either the sideffect or health degeneration to eat those rotten items.
Another thing: The efficiency upgrade reduces the original mats from 10 to 8. So a 10% green (100% = 10%*10 or 100%/10 = 10%) become 12,5%(100% = 12,5%*8 or 100%/8 = 12,5%).

A little thing for later: You need electricity to cook. When you don't want(or can) use it, it takes 1 coal. Though I don't know if this is for 1 cooking or total for batchcooking - 5 meals cooked at once 5 coal? or 5 meals cooked at once only 1.

It was a bit confusing at first for me but after using the cooking station 2-3 times I figured out the percentage is how much of a meal you would make. And that higher level cooking means higher quality meals which fills you up more. Not by much but it's well worth the investment if you choose to make more bandages and less meals out of those potatoes.

Don't know how they did the % for each item, I just only know that you need to calculate their original hunger vs. the crafted one. And that's 30 for base meal, 40 for lvl 2 meal and I can only guess 50 for lvl 3 kitchen.
Potatoes have 3 uses! 1. To craft wine(to make alcohol out of it). Rotten for a med recipe and then as planting material. Grinding them down is the best usage(with the 20% efficiency upgrade) as that takes 12 potatoes for 5 instead of 15 for 5. Though there is a recipe at outdoor campfires that you can bake potatoes. Didn't look into the values, but that could be even better for hunger.
Another thing: Cody can learn a skill that gives +1 to base stats of hunger/thirst for items. Look like it affect all items regardless if you cooked them or traded or got them any other way. That would reduce the cooking use for some items even more. Though I didn'T have on base difficulty any problems anymore with hunger(maybe a bit thirst) as I got so many items I could process into meals that I'm literally overfeed.