Tamari (Best Option)
1 teaspoon per 1 tablespoon soy sauceTamari is a gluten-free soy sauce variant with a richer, smoother umami flavor that closely mimics traditional soy sauce. It works well in Béarnaise because it enhances the savory depth without overwhelming the tarragon and shallots.
When using tamari, start with a slightly reduced amount and adjust to taste, as it can be less salty. Avoid overheating it directly to prevent bitterness.
The final Béarnaise will maintain its classic buttery and herbal character with a subtle umami boost, making tamari the closest match to soy sauce in this context.