When writing recipes is it true that native speakers use singular and plural forms when they list ingredients but when talking about them being cooked cut fried etc only the singular form is used? For example Ingredients 1 potato or 2 potatoes. 1 egg 1 carrot 3 carrots depends on how many of them are needed. 1 sausage 1 cucumber But when chopped, fried, etc only the singular as in "These salad is made with potato, egg, carrot, sausage, cucumber and mayonnaise. Not "potatoes, eggs, and carrots and sausages, and cucumbers.
Some foodstuffs are non-countable nouns, any many can become non-countable when used as ingredients. For example, you can count eggs while they are in their shell, but once several eggs are cracked and beaten you would likely refer to the mix as "egg" in singular form. A recipe might list "3 eggs, beaten" in the ingredients, but the method might then say something like "add the egg to the bowl", meaning all of the egg mixture derived from the 3 eggs.
In your example where you are referring to a "salad made with potato, egg, carrot and mayonnaise", it is fine to use the ingredients in singular form because you are not quantifying the amount of salad. You are in effect saying that any given quantity of the salad will contain some carrot, some potato etc. You only need to start specifying the amounts or numbers of ingredients when you are being specific about the amount of the end product, such as in a recipe where it might state "to make this salad for 4 people you will need 4 eggs... etc".