Whenever you search, you will get much better results if you use the filters on the right rather than the word search. The word search looks for every appearance of the words in book title, author, recipe title and ingredients, incuding any variation of the ingredient name. So a search just using pesto as search will include recipes containing pre-made pesto
If you add the filter "Sauces, general" under the filter Recipe types, Side dishes then you will only see recipes for pesto sauce - you can see this in the Library here. Some of those recipes have a pesto recipe as part of another recipe, some recipes are just for pesto sauce.
Another option is to search using the filter "Pasta doughs & sauces" under Recipes types, Dish types - you can see that in the Library here. However this search will include recipes for pasta with pre-made pesto sauce,, which is not what you want here.
There is a section in Help on using the filters here. There is also a helpful video that shows you how to use the search functions on EYB.