How do I master complex financial reporting and controls?

You can run the function now, and the complex reporting and the controls are what still trip you, the intricate statements and the systems that keep everything honest. That's the deep end of the craft. Struggling there isn't a shortfall. It's proof you've already mastered the shallower parts and reached the genuinely hard ones. Complex reporting and strong controls yield to structure and to learning from people who've done it. You break the hard report into its parts and understand each. You study the controls not as rules to memorize but as a system with a logic. And you find someone experienced to check your thinking, because no one learns this purely alone. Take the one reporting or control area that trips you most and go deep on just that this quarter, with a mentor or a solid reference at hand. Master one, and it strengthens the rest. The complex parts are where controllers are made, and you're standing right at that edge.