We had several failures before our first success. Allow me to tell you how we "discovered" what we were doing wrong. Attempt 1: Egg was whisked in a bowl first then added to small food processor. The oil was added rather quickly (over about 1 minute) at a constant rate. It never thickened and looked quite nasty! Attempt 2: We thought that perhaps the egg yolk was not beaten enough before the addition of oil, so the yolk was whipped for a long time first. However, we had the same result after same addition rate of the oil. Attempt 3: Chilled all ingredients first, repeated attempt 2. Same result. Attempt 4: At this point we thought that perhaps the food processor was mixing too aggressively, so we decided to try making it by hand in a bowl with a whisk. We added the oil extremely slowly: perhaps <1/4 tsp at a time and then whisked until it was visibly thickened. Once the thickening was started, we discovered that it was possible to add the oil much faster, perhaps as much as 1/4 cup at a time. After a short time of mixing by hand we switched to an emersion blender with a whisk attachment and had great success. I think that probably our initial conclusion that the food processor was too aggressive is incorrect, and that the addition rate of the oil is much more important. From an ergonomics standpoint, we found that using a drinking glass and an emersion blender with the whisk attachment was the most effective way to do this. The glass was just slightly larger than the diameter of the whisk, so it was possible to churn the entire mixture easily. The speed and power of the blender seemed perfect for this task. We never really did get the food processor method to work properly, and the cleanup from this method was quite easy!