Numerical Optimization, Jorge Nocedal and Stephen J. Wright, 2006 (Springer)DOI: 10.1007/978-0-387-40065-5 - A widely recognized textbook providing a rigorous and thorough treatment of L-BFGS and other optimization methods.
Optimization for Machine Learning (Lecture Notes), Jonathan Richard Shewchuk, 2005 (University of California, Berkeley) - Educational notes offering a clear derivation and explanation of the L-BFGS algorithm, including its two-loop recursion.