You can't really "call a recipe from another". When you develop a custom recipe in a plugin, you are actually developing a new "type" of recipe. Whereas the only thing that could be called is an "instance" of a recipe, that you don't know about at development time.
It sounds however that what you want to achieve is to share some code between both your recipes, so that common functions don't need to be written twice. This is possible through the "python-lib" folder of the plugin: https://doc.dataiku.com/dss/latest/plugins/reference/other.html#shared-code