Wash 1 pound fresh tomatoes, cut them into wedges, and place them in a bowl.
Peel ½ small yellow onion, chop it finely, and add it to the tomatoes.
Pour 4 Tablespoons cold water, 1 Tablespoon apple cider vinegar, and 1 Tablespoon olive oil into a small jar with a screw-top lid. Add 1 teaspoon granulated sugar, ¼ teaspoon salt, and 1 dash ground black pepper, close the jar, and shake until blended. Taste and adjust the seasoning if needed.
Pour the dressing over the vegetables and stir gently. Serve right away or chilled.
Notes
No kitchen scale? One medium tomato weighs about 5 oz (150 g); for the basic recipe you need about 3.
Vinegar: This recipe was developed with apple cider vinegar at 5% acidity. Czech vinegar has 8%, American distilled white vinegar about 4%; with a stronger or weaker vinegar, adjust the water and sugar to taste.
Tomatoes: Use fully ripe but firm tomatoes; their flavor carries the salad.
How to eat: Serve the salad in its own small bowl beside the plate. Eat it with a small spoon, and feel free to drink the leftover dressing like a Czech.
Store: Best fresh. Keeps covered in the fridge until the next day, but the tomatoes soften. Do not freeze.