Hi,
It has been known to me that a gerund can function as a noun and should or likely to be treated more as an uncountable noun than a countable noun.
Mixing of sugar and flour makes this dough ...
If you want to be specific, I think you could write:
The mixing of sugar and flour makes this dough ...
If you want to indicate the mixing being an instance of it or an example of it, you could write (I think) like this:
A mixing of sugar and flour makes this dough ...
It could be more clear if you write this though (but the above example seems to be correct grammatically too):
An instance of sugar and flour makes this dough ...
It has been to me that a quoted content (I may be wrong but what I call a quoted content is one that has quotation marks around it, whether or not they are done to quote someone's words or to highlight a word/words) can be treated an uncountble noun too.
"-ing" is not needed in your sentence. -- Just the mention of a case to highlight, I think.
The "-ing" is not needed in your sentence. -- Not just mentioning but specificallymentioning, I think.
A "-ing" is not needed in your sentence. -- An example of "-ing" use or an instance of "-ing" use, but this is what gives me trouble. I think whether a word in quotation marks can accommodate an indefinite article is predicated on whether its semantic meaning can embrace it.
So, I think I would be able to say, depending on words, some words that are in quotation marks can accommodate its having an indefinite article, whereas some words that are in quotation marks can't accommodate the use because its semantic meaning and how it is used in sentences make it awkward at best if not wrong to have an indefinite article. Sounds plausible?
Sorry for a long post.