Measure out the two oils and have ready. Whisking the egg mixture, slowly, in a very fine stream, add the oil to the center of the bowl, Keep whisking as fast as you can, watching the egg mixture dissolve the oil into itself. The mixture will start to thicken the last 1/4 cup of oil. Extra large egg yolks can emulsify up to 1/2 cup of oil, per yolk. This is also when the mayonnaise will be the right consistency.
The mayonnaise is done when the whisk leaves a trail of where the whisk was, like a thick custard. Using a spatula, transfer the finished mayo to a pint Mason jar (or other seal-able container with a 1 1/2 cup size) and seal with a lid. The mayo will thicken slightly more, once refrigerated.