There are several options.
Perhaps the easiest is to use separate code fences like this:
```
code
```
```
separate code
```
Which produces this:
code
separate code
Another way is to insert a line rule by putting three (or more) hyphens/dashes (---) on an empty line, without indentation, between the blocks, which produces a sharper separation:
code
separate code
(this can be used with indented code blocks as I've done here, or in addition to separate code fences as shown in my first example)
With indentation you can also use an unindented <br> tag, or better, as noted by muru a html comment <!-- --> to force a break (this also works in list context), which does this:
code
separate code
or
code
separate code
NB: In case it's useful, those with 2k reputation can click the edit button under this post to see the markdown. Since there is no facility to suggest edits on meta, I have pasted the markdown text here for those who don't have 2k reputation.