1. Soak the Onion:

• Place the thinly sliced red onion in a small bowl.
• Cover the onion slices completely with cold water.
• Let them stand and soak while you prepare the rest of the ingredients, about 10 minutes. This step significantly mellows the onion’s raw bite.

2. Prepare Tomatoes and Herbs:

• Core the heirloom tomatoes. Slice them into 1/2-inch-thick wedges or half-moons, depending on their shape and your preference.
• Place the sliced tomatoes in a large serving bowl.
• Coarsely chop your chosen fresh herbs and add them to the bowl with the tomatoes.

3. Assemble and Dress the Salad:

• Drain the soaked onions thoroughly and add them to the bowl with the tomatoes and herbs.
• Drizzle the extra-virgin olive oil and red wine vinegar over the salad ingredients.
• Sprinkle with the 1/2 teaspoon kosher salt and 1/4 teaspoon freshly ground black pepper.
• Gently toss everything together until the tomatoes and onions are evenly coated with the dressing and herbs.

4. Let Stand (Macerate):

• Let the salad stand at room temperature for at least 10 minutes, or up to 30 minutes, before serving. This allows the flavors to meld and the tomatoes to release some of their delicious juices into the dressing.

5. Adjust Seasoning and Serve:

• Just before serving, taste the salad. Adjust with more salt, pepper, vinegar, or olive oil as needed to reach your desired balance.
• Serve the tomato salad immediately.