Measure the vinegar into a clean glass jar. Defrost the strawberries on a glass plate in the microwave for about a minute, or just set on the counter until they defrost and release some of their juices. Using your fingers, crush the strawberries and add them and any juices to the vinegar. Rub the mint leaves with your fingers to bruise them and release some of their fragrant oils, then add them to the vinegar, pushing them down into the jar.
Cover the jar and label it with the content and date. Set it on the counter by a sunny window for 1 to 2 weeks, shaking it daily. After a week, taste it. If you like the intensity of the strawberry and mint flavor, it’s ready, or if you prefer a stronger flavor, let it stand for another week.
When the mixture has steeped to your liking, use a fine mesh strainer to drain the vinegar into a bowl. Use the back of a wooden spoon or your fingers to press out as much juice from the berries and mint as you can. Discard the berries and mint, or puree them in the blender with alittle olive oil, sea salt, and pepper and use on your tossed salad later in the day.
Pour the strained vinegar into a clean bottle. Cover and label it with the recipe name and date.