Backtesting Expected Shortfall

Hi I have a question regarding Backtesting Expected Shortfall… ES is computed by taking average of losses beyond VaR assumption (say 99%) . We backtest VaR by taking actual P&L and checking how many times it has exceeded ? But how do we backtest Expected shortfall? do we take only actual P&L which breached VaR and look at the average loss? im confused. :(