Chicken Broth (Best Option)
1/4 cup per 1/4 cup beef brothChicken broth contains amino acids and glutamates similar to beef broth, which contribute to the umami and savory notes essential in Béarnaise sauce. Its lighter flavor profile allows the tarragon and shallots to remain prominent without being masked.
When using chicken broth, ensure it is low-sodium to avoid overpowering the delicate flavors. Heat gently to avoid breaking the emulsion of the sauce.
The final Béarnaise will be slightly lighter in flavor but still rich and balanced, making chicken broth the closest and most reliable substitute for beef broth in this context.