A shallot reduction is at its heart an infused vinegar that has been boiled down until most of the liquid has evaporated, leaving behind a concentrated concoction. This flavorful mixture is what adds the bulk of the flavor and tang to béarnaise sauce, and cuts through the richness of the butter to create that moreish bite. This shallot reduction is the main component that differentiates hollandaise sauce from béarnaise, so it’s safe to say this is one of the most important parts.

To make the shallot reduction, start with a saucepan filled with finely chopped shallots in white vinegar. Some recipes also call for white wine, but this is optional and won’t affect your final sauce too much either way. You slowly heat that up, along with your herbs like tarragon, and black pepper. Keep the mixture at a steady simmer for as long as it takes to reduce the liquid to just about 3 tablespoons. Even less liquid (up to a tablespoon) is also acceptable as the flavor is all there in a condensed form.

This reduction needs to cool completely before moving on to the next step of adding egg yolks. It’s then your preference whether to strain out the remaining liquid with a sieve or to use the lumpy mixture altogether, depending on whether you want a more refined or rustic béarnaise sauce to serve.