Are you talking about the text in the entry-content div? You can see the html, of course, with either the Develop menu or just by saving a page with a recipe on it with Safari->Save as... "Page source". Either way will show you the CSS styles specified for the various parts of the page.
The html starts at the html tag and proceeds as follows: 1 <head>...
2 <body> with six different classes defined,
3 one of which installs the font you dislike
4 "custom-font-enabled"
5 <div id="page" class="hfeed site">
6 <header id="masthead" class="site-header"...
7 <div class="wrapper" id="main">
8 <div id="primary" class="site-content">
9 <div id="content"...>
10 <article id="" class=""
[way too many classes!!!!]
11 <header class="entry-header">
12 <h1 class="entry-title">
[link and a text for the title
such as "No Bake Chocolate
Raspberry Dessert"]
lots of stuff
13 <div class="entry-content">
14 <p><em>[description of recipe
in your favorite font?
You can always create your own CSS file and list it in Safari's prefs->Advanced: "Style sheet". Store it just about anywhere on your drive and point to it with the "Other..." choice.
I think you might get what you want by trying to over-ride the classes mentioned in lines 10 and 13 above. You could simply create a style sheet redefining "entry-title" and "entry-content" with your own font stack:.entry-title, .entry-content
{ font-family: helvetica, monaco, sans-serif; }
The font choices are yours, of course, but you should stick with ones on your OS install.
Write the above text in TextEdit and make sure to save it as .txt (not .rtf) with an appropriate name then change the suffix to ".css". Go back to Safari and use the Advanced Pref to point to that file.
Theoretically, the only thing that css file will do is over-ride any text, in any file that uses a class named "entry-title" or "entry-content". Hopefully, that recipe site will be the only one that you visit that has those two classes declared. There are ways to make these a bit more specific which may also help in making them over-ride the site's css.