Hollandaise and béarnaise sauces make use of butter, egg yolk, and some kind of acidic ingredient. However, béarnaise sauce is a bit more complex than its popular predecessor.

Béarnaise sauce incorporates white wine vinegar instead of lemon juice and has shallots, tarragon, and other herbs, making it much more herbaceous while also thinning the texture.

Both sauces are similar in taste; you can create béarnaise sauce out of leftover hollandaise sauce by reducing the latter and adding the extra ingredients for béarnaise.

It’s not exactly a one-for-one exchange, but it shows how similar these two sauces are and how béarnaise may have been developed from hollandaise from the start.