Hi Mireille and welcome to Eat Your Books
There does seem to be an issue with that recipe - I found it online at the Emile Henry site. Every recipe on that site causes an error when I tried to add them. Sometimes sites block other sites from capturing the information, which I think they have done here.
I got around it for you by cheating. You can now add it to your Bookshelf from here. I will investigate further why the error happened and I will contact Emile Henry and let them know they are losing traffic to their site by not allowing other sites to link to the recipes. In the meantime, if there are other recipes from the site you want added you can contact Christine at [email protected].
You insert a URL in a Forum post (as I did above) by highlighting the text where you want the link then click the link icon in the row above the text box (the 3rd from the right) which becomes visible once you have highlighted the text. If you are linking to a different site we request that you open it in a new tab - the third box down labelled Target.
Finally, you cannot add HTML in your post text - as you can see, it displays.