Question

Currently the user can add a single ingredient to a recipe, but that relational key is then bound to that one recipe, changing it to a new recipe, removes the old link.

I am looking for a method so a single version of each ingredient exists, but any recipe can contain it

Answer 1

You should have separate Recipe, Ingredient, and RecipeIngredient tables.

Ingredient
----------
IngredientID <-- PK
Name
...


Recipe
------
RecipeID <-- PK
Name
...


RecipeIngredient 
----------------
RecipeID     <-- PK
IngredientID <-- PK

This is basic database normalization.