Homemade mayonnaise tastes fresher and brighter than anything you can buy at the store. This version is flavored with anchovies and Parmesan cheese.
If the mayonnaise separates after the oil is added, the mixture has broken. To bring it to a creamy state, add an egg yolk and 1 teaspoon tepid water to a clean bowl, and slowly add the broken mayonnaise while whisking constantly. Then, whisk in 1/4 cup more oil.