How to type a long/em dash `—`

When writing emails and articles I often find myself in the need to use a long/em dash — character, not to be confused with the hyphen - character. Normally what I end up doing is I type two consecutive hyphens -- and hit the Space key, which then ends up replacing the two hyphens with the long dash.

However, when posting articles in browser-based editors this doesn't always work — such as with the post editor here — so I have to type the double hyphen + Space elsewhere, like in a dummy email, copy the long dash from there and paste it here. This is very inconvenient of course.

I'd like a shortcut to enter the long dash character directly.

This might be one of those that changes by language, but on a UK English keyboard [& from comments, also US English], there are 4 dashes available from the key to the right of 0, Minus.

- - key alone (hyphen)
– - Opt ⌥ (en dash)
— - Opt ⌥ Shift ⇧ (em dash)
_ - Shift ⇧ (underscore)

Late Edit...
To complete the set, & from comments...

Ctrl ⌃ Opt ⌥ - will give 'information separator one' which looks like a space "" & doesn't even seem to print in here. You could, however use the keyboard replacement tool to turn that into a true minus sign... −

After some digging around I've found that Alt+Shift+Minus renders the long/em dash (—) character.