You can prepare this recipe with an immersion blender, a regular blender or a food processor. If using an immersion blender, layer all of the ingredients carefully in a large-mouth jar, starting with the egg, egg yolk and mustard, then slowly adding the lemon juice, vinegar, salt and pepper and finishing with the MCT and avocado oils. Lower the immersion blender all the way to the bottom of the jar. Without moving the blender, turn it on, on a slow setting, and run it until all the ingredients have blended together and mayonnaise has formed.
If using a blender or food processor, blend the egg, egg yolk, mustard, lemon juice, vinegar, salt and pepper until well combined. With the blender still running, add the oil in a very slow, thin, steady stream and blend until the mayo is thick and smooth.