Most of the workouts I know for biceps/triceps only involve one or the other. Never both. But if there is one out there, could someone please tell me?
Biceps and Triceps are antagonist muscles. That means when one is the primary mover, the other simply lends stability. The concept that an exercise is for a particular muscle group simply means that the primary movers do most of the work.
Because they are antagonist muscles the only thing that can hit them about the same is a static hold for time. Even then, depending on whether your arms are extended (triceps) or flexed (biceps), the majority of the work will still be one or the other.
As stated by @BerinLoritsch, you cannot work both at the same exact moment. You can, however, achieve muscle engagement of both by doing muscle-ups. They are difficult if you're just starting out and will probably require steady pull-up progression before they can be achieved. Here's a video of how they've performed. You'll use your biceps to get you to the bar, and the triceps will push you above it. There are multiple other muscles worked, but this exercise does meet your question specifics.