If you don't have a BS degree, get one. It will take a while, but the money from your employer should pay for 2 classes a semester at a state school. (Thanks Boeing!)
My suggestion, at about the 10 year mark in experience, get an MS degree (or and MBA, if that is your thing). My MS took 5 years as the tuition reimbursement covered only 2 classes per year at the school I chose. (Thanks L3 Communications!)
None of the classes I took made me "an expert in something at work". The sum of all the classes, arguably, made an attempt.
Diff Eq. Calculus. Linear Algebrae. Data Structures. Software Requirements. Theory of computation. All of them fill in the space between what you have figured out on your own and what you need to know. And allows you to build on to bigger things.
