Bench vise. Last time this happened I disassembled the pedal down to the spindle, then just took the crank arm with stuck spindle to the LBS since I don't have a workshop with bench vise anymore. They tried a long wrench too, no luck. I think they clamped the spindle in the bench vise and used a cheater pipe on the crank arm. Whatever, it worked.

Now I'm careful to grease the threads and avoid overtightening pedals.