The cost per portion of the main ingredient is used to determine the cost of the dish. The cost of all the ingredients in a dish must be determined to get a total cost for the item. This works well with items on an à la carte menu where the basic ingredient is sold by itself and traditional add-ons are sold separately. The total cost of a dish can also be calculated by multiplying the cost per kilogram by the number of ingredients.
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References
https://totalfood.com/calculating-food-cost/