This citrus-based sauce adds low-sodium flavor to salads, chicken, or seafood.
Using the smallest holes of a box grater, remove zest from 1 lemon; set aside. Squeeze juice from both lemons, yielding 4 tablespoons. In a small bowl, whisk together buttermilk, yogurt, zest, juice, and shallot; season with salt and pepper. Store in an airtight container, refrigerated, up to 3 days.