Using a bread knife, trim top and bottom of brioche rolls. Cut rolls in half to create 24 flat rounds.

Spread each round with a thin layer of mayonnaise. Top half of them with slices of onion and sprinkle with salt. Cover with remaining round of bread. Press them together gently and spread a thin layer of mayonnaise around the edges. Roll each sandwich in the chopped parsley.

Place sandwiches in a single layer on a platter and chill for several hours before serving.

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Adapted from James Beard's original recipe. Recipe photo and food styling by Judy Kim.