Highlight the text you want to use as a link and click on the link icon on the toolbar at the top right of the recipe popup.
The standard WordPress link popup will open and you can enter a link URL or select from one of your existing posts/pages. Once inserted, the image will show in the recipe popup like:
[url:1]my link text[/url]
It will converted to a proper link when the recipe is displayed.
To insert a link you can manually enter the [url] shortcode. The [url] shortcode works just like the HTML <a… > tag. So for example, at the place where you want the link to appear you might add something like:
[url href="http://somesite.com/page.html"]A page at somesite[/url]
You don’t need to use the Text/HTML editor – you can add that right in the recipe popup.
You can use anything inside the [url] shortcode tag that you can use inside an <a> tag. So you could have something like:
[url href="http://somesite.com/page.html" target="_blank"]A page at somesite[/url]