[Richard Flynn]

With no rows displayed in the Quick Entry panel, you can press shift+return to display a new blank row.

This is the same shortcut that you can use to add more than one entry at once in Quick Entry. AFAIK this is the only way to add more than one task in Quick Entry; strictly shift+return is 'Add row above' and so the second task appears above the first. I personally wouldn't mind seeing another shortcut for adding a row below (but let's keep return on its own to save and close the Quick Entry window—it was a pain when this shortcut was turned off a few months ago and the only way to close Quick Entry was Cmd+S).