Make sure that you don't skip lemon juice as it works as a stabilizer. If an emulsion is broken, you can try fixing it by adding a boiled potato or 2 egg whites to the food processor leaving just a quarter of the broken emulsion and blend. Then gradually add back in the broken emulsion. This should help to emulsify the sauce. If a potato or egg whites are used, you can store the sauce in the fridge for just 5 days.