Crack an egg into a jar wide enough to accommodate an immersion blender.
Add the juice and salt, and then pour in 1 cup of extra light tasting olive oil. Wait a few seconds, until the egg is resting at the bottom of the jar, just beneath the oil, and then press your immersion blender all the way to the bottom of the jar, push the power button, and keep the blender steadily pressed to the bottom of the jar for about 20 seconds. Suddenly, mayonnaise will start to magically appear — first at the bottom of the jar, then it will seem to “climb” to the top.
*In a sealed jar, the mayonnaise will keep for about 2 weeks.