Here is a longer introduction: http://perl.atitd.wiki/wiki/tale3/Guides/Cooking
Remember to use the copper pot in your kitchen, not an iron one.
All cooking ingredients have a corresponding position on a 2000 by 2000 square. Various people have measured some positions, but for almost all ingredients, they were measured most comprehensively and precisely by Quizzical, who also suggested the scheme in the first place. See here for the coordinates: http://perl.atitd.wiki/wiki/tale3/Users/Kummick/PotencyTable and here for a very nice visualization: http://perl.atitd.wiki/wiki/tale3/Cooking/Herboverlay
Remember that the distance between two points is D = squareroot((X1-X2)^2 + (Y1-Y2)^2).
There are two kinds of ingredients in a recipe: Base and additive. You can use as many base ingredients as your cooking level, and a maximum of 21 ingredients. A base ingredient is one that is tied for the most deben in a recipe. Additives are everything else. Each additive will pair with one base, the closest to it. The strength of the effect of an additive depends on how far away it is from the base and on the potency of the additive.
The stats you get out of a recipe depend on the coordinates of the ingredients and on the characteristic pluses and minuses and the potency of mostly the additive ingredients, very slightly on the potency of the base ingredients. Each ingredient has a plus or a minus to one or more stats, never more than 2 pluses or two minuses except for one ingredient that I know of, oysters. Oysters are also peculiar in that they have twice the effect on endurance that they do on strength and dexterity. Everything else has the same effect (as far as I can tell) on stats they affect at all. Now and then you see a small effect on a stat you didn't expect. Usually that is from the base ingredient(s), but possibly additives could have small additional effects on stats they don't usually affect. Note that using multiple deben of an additive does not change the stats you get from a pair, only possibly the duration from its potency bonus. So don't use multiple deben of additives. It will reduce the potency of the additive.
Potency varies, apparently depending on how much of an ingredient has been used in cooking throughout Egypt. It is higher for herbs than other ingredients, unless the herb is used a lot. It is higher for ingredients that are used very little, either because they are rare, subtract from stats people usually want to add to, or because they don't appear in commonly circulated recipes.
You can describe potency of an additive in terms of the number it increases a stat, but that varies by what base you pair it with. The number I use is measured in seconds, and it is the difference between the time a recipe lasts and what it would last with zero potency, divided by the fraction of the meal the additive is. For instance, if I make a meal of 6 mutton and 1 acorn's cap, it lasts 16 minutes and 20 seconds or 980 seconds. From the formulas for meal duration based on distance between ingredients, it would last 706 seconds (the distance between the coordinates of mutton and acorn's cap, which happens to be 294. The formula is: duration = 1000 seconds - distance). So, the potency of acorn's cap is 980-706 = 274 seconds divided by 1/7 (there are 7 deben total of stuff in the meal, and acorn's cap is 1 deben), or 1918.
Here is a table of potencies, for a particular time (around December 5, 2006):
http://perl.atitd.wiki/wiki/tale3/Users/Kummick/PotencyTable
Remember that these will change as people cook with different things.
For a simple recipe, with only one additive per base, with the bases selected so that they are the closest one for only that one additive and not any of the others, the duration is the duration of each pair added up.
So if you know the coordinates of the ingredients and potency of the additives, you can figure out beforehand the time the recipe should last.
The duration for a recipe with multiple additives per base is the total of the times for each base/additive group. The time for a base and its additives is (1000 seconds minus the total of the distances between the base and each additive) / number of additives. Notice that the time decreases rapidly with number of additives per base. I'm not sure of this yet, but the potency bonus seems to be about the total of the potency bonuses of the additives.
For a simple pair, the stat boost is given by sqrt((1000-distance) * potency/17200). The maximum potency for herbs appears to be approximately 17200, and the maximum for other ingredients appears to be 1/4 of that, or 4300. [Maybe that should be 4400, that I just measured for oysters] Note that using multiple deben of an additive does not change the stats you get from a pair, only possibly the duration from its potency bonus. So don't use multiple deben of additives. It will reduce the potency of the additive.
NEW: Potencies seem to have started to increase about the time the new herbs showed up. The maximum potency is now greater than ~17200, and some of the rare, unlikely to be cooked (only negative stats) old herbs are up in the ~19000 range. Many of the new herbs are reported to be ~20000 http://perl.atitd.wiki/wiki/tale3/Users/Tactician/NewHerbs/Coords. I have found lower values, so I think that it only takes a few deben cooked anywhere in Egypt to lower the potency quickly from the maximum. The factor in the expression to determine stat bonus still is about 17200.
When there is more than one pair that contributes to some stat, the boost is given by the square root of the sum of the squares of each pair's boost.
Where there is more than one additive pairing with a base, the distance that goes into the above formula for ALL additives paired with that base is the MAXIMUM of the distances for all additives paired with that base. For example, suppose I use a base of 5 chicken, with 2 additives, 1 common rosemary and 1 cinquefoil. The distance of cinquefoil to chicken is 171, and the distance of rosemary to chicken is 580. So the distance to the rosemary is the one that counts, and it is used to calculate the contribution for both the rosemary and the cinquefoil. The potency of cinquefoil is 8082, and the potency of rosemary is 1638. Cinquefoil contributes to speed and rosemary doesn't. The stat boost that cinquefoil gives to SPEED is
sqrt((1000 - 580)*(8082/17200)) = 13.
Since the distance of cinquefoil to chicken is much less, by itself the chicken-cinquefoil pair would give a boost of 19.
Both ingredients contribute to END. The total boost is the squareroot of the sum of the squares of the individual boosts:
sqrt( (1000-580) * (8082/17200) ) + (1000-580) * (1638/17200) ) = 15
So this is not a good selection of base and multiple additives if you want to maximize END, because it is less than one of the additives by itself. You need to select bases that have a similar distance to all additives that they pair with, and make that similar distance as low as possible.
Note that the square root of the sum of the squares rule applies to all additions to a stat, both for pairs of additives with different bases and pairs of additives with the same base.