Place the egg, lemon juice, salt, and any flavorings into a bowl.
1 large egg, 1 tablespoon lemon juice, 1/4 teaspoon salt
Using a hand whisk, mix until it is thoroughly combined.
While still whisking, slowly drizzle the oil into your egg mixture. Drizzle slowly enough that the oil is incorporated and emulsified rather than being mixed around.
1 cup olive oil
Once all the oil is added, continue to whisk until the mayo has thickened up a bit, another two to three minutes.
If using a food processor:
Place the egg, lemon juice, salt, and any other ingredients in the bowl of your food processor.
Turn on your food processor and mix for five seconds. Scrape down the bowl.
While the motor is running, slowly drizzle in the oil. Once the oil is all added, turn off the food processor and again scrape down the bowl.
Mix one last time to ensure the mixture is a uniform texture, but don't overwhip the mayo.
If using an immersion blender:
Place all ingredients into a tall, narrow container.
Place the immersion blender into your container all the way to the bottom. Mix at high speed until the mixture has emulsified, which will take seconds.
As the bottom emulsifies, carefully and slowly raise the blender near the top to get all the oil in the container emulsified into your mayonnaise.
Once your mayonnaise is made, you can serve immediately or store in a sealed container for up to a week. Note that it will start out a little thinner than store bought mayonnaise but will firm up in the fridge.