Ruhlman's 20 was that book for me. From that one book I feel like I can dissect and understand so many core concepts that I very rarely follow recipes any longe

Ruhlman's 20 was that book for me. From that one book I feel like I can dissect and understand so many core concepts that I very rarely follow recipes any longer, I just skim for the key aspects and wing it, substituting with what I have available, and a reasonable intuition for when I can't do so. Am grateful I made that investment (reading it, making most of the recipes).