Place one room temperature whole egg along with two egg yolks in a mason jar. Add mustard, lemon juice, apple cider vinegar and a pinch of salt. Turn the immersion blender on high speed. Blend until the mixture becomes light and frothy, about 30 seconds to 1 minute. With the immersion blender on high speed, pour olive oil in a thin stream or even 1 drop at a time until you’ve poured in ½ of the amount needed. *If you rush this process then the fat from the yolk will not take in the fat from the oil, therefore causing your mayonnaise to separate! Once about ½ of the cup of olive oil has been incorporated (your mayonnaise should be getting thicker by now, if not keep adding 1 drop at a time), you can add a bit more olive oil at one time until the remaining cup of olive oil has been blended in. Salt and pepper to taste. Add to your favorite dish!