Whisk thoroughly till the mixture turns pale and become frothy (foamy)

Then it's time to add the oil, a little at a time.
I usually put this in a dropper bottle or you can pierce a hole in the cap of a water bottle, pour the oil into and cover tightly.
Make sure that the bowl is well balanced cause you'll be using one hand to add the oil and the other to whisk the mixture.

Start adding the oil drop by drop whisking all the way till the mixture starts to thicken. You can then increase the quantity of oil you add as you whisk till you exhaust it.