In the bowl of a food processor or a tall container suitable for an immersion blender, combine the egg yolks, Dijon mustard, and 1 teaspoon (5 ml / 0.2 fl oz) of the lemon juice. Pulse a few times until the mixture is smooth and slightly frothy.
With the food processor or blender running on low, begin adding the liquid fat *extremely* slowly, just a few drops at a time.
Once you see the mixture start to thicken and emulsify, you can increase the stream to a very thin, steady trickle until all the oil is incorporated.
Once all the oil is added and the mayonnaise is thick and creamy, turn off the machine.
Stir in the remaining 2 teaspoons (10 ml / 0.3 fl oz) of lemon juice.
Season generously with salt and pepper to your liking.
Transfer the mayonnaise to an airtight container or jar and store in the refrigerator for up to one week.
When using coconut oil, be sure to choose expeller-pressed or refined coconut oil. These versions have a neutral flavor, unlike virgin coconut oil.