1Stir mayonnaise with the yogurt and mustard. Wash the lemon with hot water and finely grate about 1 teaspoon rind. Cut off some of the rind and cut into thin strips. Squeeze 2 tablespoons lemon juice and mix into the mayonnaise with grated rind.
2Season with salt and pepper. Divide among 4 small bowls and garnish with strips of rind.