Melt the butter in a saucepan with the flour to make a blond roux.
Place the roux in the work bowl and while processing add the hot stock.
Work until smooth.
Return to the saucepan.
Cook the sauce for 5 minutes.
Return to work bowl and while processing add the lightly beaten eggs, lemon juice and water.
Return to the pan and heat, but do not boil as this will cause the sauce to curdle.