You can insert links to other recipes anywhere in your ingredients or directions using a special syntax. To link to another recipe, put the name of the recipe in brackets, and prefix it with
[recipe:Brussels Sprouts with Pancetta]
These special links will automatically be detected when the recipe is displayed.
Note: You can also use the text editing toolbar to choose a recipe and it will insert the link for you. Just tap on the insert recipe button and select the recipe.
(This screenshot is from the iOS app but there are equivalent buttons in the Android, Mac, and Windows versions.)