When I'm in the mood for zhuzhing, I add ⅛ teaspoon of dry mustard or a lightly rounded ¼ teaspoon of Dijon mustard along with the red wine vinegar. Mustard helps to emulsify a vinaigrette, and just a hint of this sharp, tangy ingredient provides subtle balance to the sweet summer tomatoes.
In a small bowl, combine the garlic, oregano, and vinegar. Set aside.
Sprinkle a lightly rounded ¼ teaspoon salt evenly over a serving plate. Slice the tomatoes (about ¼-inch thick) and arrange them on the plate. Sprinkle with the red onion. (Helpful hint: For more direct contact with the salt and the vinaigrette, I like to use a plate that is large enough to hold at least half the tomatoes in a single layer.) If there is tomato juice on the cutting board, drizzle it into the vinegar mixture. Then sprinkle another ¼ teaspoon salt and black pepper, to taste, evenly over the arranged tomatoes. (I’m generous with the cracked pepper—I’d say I use about ½ teaspoon.)
Whisk the olive oil into the vinegar mixture and spoon it evenly over the tomatoes, scraping out all the garlic and oregano. Sprinkle with flaky salt, basil, and/or chives, if using.
Notes
I like the classic, full-bodied flavor of a beefsteak tomato in this recipe but often add a yellow or heirloom tomato and/or a handful of halved cherry tomatoes for variety and visual appeal.
Dried oregano works quite well in this recipe, but if you have fresh, feel free to use 1½ teaspoons.
Sometimes, I add ⅛ teaspoon dry mustard or a lightly rounded ¼ teaspoon Dijon mustard along with the vinegar for subtle depth to the tangy vinegar.