This is a lovely, spicy, warm flavored sauce that can be adapted by adding other ingredients. I often stir in hard-boiled eggs or bread crumbs soaked in vinegar, which adds different textures.
Serve with fish, cooked meats, cheese and salads.
Put the mustard leaves and garlic into a food processor and blend with 2 tsp vinegar. With the processor still running, add the olive oil in a slow stream, season to taste, then add the remaining vinegar if required.
Reprinted with permission from Jekka's Herb Cookbook by Jekka McVicar, Firefly Books 2012.
Trevor Corson, author of The Story of Sushi, says skip the soy sauce and extra wasabi with your sushi so you can taste the fish.