Yes, I have stalled a glider in a very steep turn at 80 knots. The nose dropped out of the turn whilst still maintaining the bank angle, just the same as a level stall, neither wing stalled first because the turn was balanced. All it required was to pull too hard trying to tighten the turn. Recovery was the same, nose "down" maintaining most of the bank until unstalled then continue the turn, not so aggressively.