With an immersion blender, mix 1 egg yolk, ½ teaspoon salt, ½ teaspoon Dijon mustard,½ teaspoon ground black pepper, 1 tablespoon lemon juice, and 1 cup olive oil on high speed.
1 egg yolk, 1 cup olive oil, ½ teaspoon salt, ½ teaspoon Dijon mustard, ½ teaspoon ground black pepper, 1 tablespoon lemon juice