This is a very highly rated cookbook, which has not been this inexpensive since 2014. It's $2.99 right now, just above 20% of the digital list price.
How high are the ratings? At Amazon 4.6 (91); at GoodReads 4.29 (42). Wow!
The book is Modern Sauces: More than 150 Recipes for Every Cook, Every Day, by Martha Holmberg and Ellen Silverman.
Oh, and it's a good-sized book at 256 pages.
https://www.amazon.com/dp/B009SM6LE0.