TIP: You can use this recipe to make your own flavor combinations, but generally speaking, stick to the one egg to one cup of oil (total) ratio.
Ingredients
1 tablespoon balsamic vinegar
1/2 teaspoon minced garlic
2 anchovies, chopped
1 large egg
1/4 teaspoon kosher salt
1/2 cup grapeseed oil
1/2 cup olive oil
Directions
In a food processor, blend together the balsamic vinegar, garlic, anchovies, egg, and salt. (See Cook's Note.) Process until well combined. With the machine running, very slowly stream in the grapeseed and olive oils until the mixture is emulsified and homogeneous. This should take 2 to 3 minutes. Maintain a slow stream throughout the entire process. Listen for a slapping sound as the mixture thickens -- that indicates the emulsification is building. Adjust the salt to taste.