You need three blank lines in a row to have a blank line register with Markdown IIRC. It may help to enable the heuristics 'format scene breaks' option as well.
As to your request - there is no simple way to do that using text as an input document. If you want to stick with text as your base format (and this is not a bad way to go by any means) then I suggest you learn a bit more about
Markdown and/or
Textile.
Markdown is a bit less techy but not quite as feature rich as Textile.