Wash tomatoes, then use a wooden skewer to poke a few holes in each one.

Place tomatoes, garlic, peppercorns, thyme sprigs, and bay leaf in a sterilized 1-pint jar.

In a saucepan, combine vinegar, water, salt, and sugar. Bring to a boil and stir until salt and sugar dissolve. Pour the hot pickling liquid over the tomatoes (leaving ½ inch of headspace). Cover jar with a new lid and band. Let cool to room temperature, then refrigerate for at least 2 days to develop flavors. Keep refrigerated, best used within 2 weeks.