How to scale Indian cooking?

Cooking is as a rule of thumb more forgiving when you tinker with the ratios than e.g. baking. That said, if you have a recipe that works and you want to increase the number of servings, the first step is to increase all ingredients by the same factor, keeping the ratios consistent. This should bring you at least into the vicinity of the desired results.

Unfortunately, this can still be somewhat off target, as recipes depend not only on ingredients, but on basic physics (and chemistry), e.g. evaporating a percentage of liquid, or heat transfer to and from a body of food, may it be a roast or a pot with a given volume. A shallow layer of something in a wide pan will cook differently than the same amount in a tall and narrow pot. Whenever you scale up or down, you need to take these factors into account. And yes, this can influence not only the cooking time, but also the flavor profile. Just think of frying a small amount vs a large amount in the same pan - there’s a reason some recipes recommend searing some ingredients in batches.

It’s almost impossible to give a generic answer, but if you follow the principles of

• scale proportionally
• determine cooking time by doneness or desired intermediate states, not time alone
• optionally, adjust liquids according to surface area

you shouldn’t be too far off and only need minor tweaks. Everything beyond that would need looking into the specific recipe.