Prepare the strawberries by washing them thoroughly, removing the hulls, and cutting them into quarters. Make sure to discard any berries with mushy spots or mold.
Combine the strawberries and sugar in a large, non-reactive bowl. Using a potato masher or wooden spoon, gently crush the berries to release their juices and mix well with the sugar until evenly coated.
Cover the bowl with plastic wrap and refrigerate for at least 6-8 hours or overnight. This process, known as maceration, will draw the juices out of the fruit and create a vibrant syrup.
Add the vinegar, basil, lemon juice, and salt to the strawberry mixture after the maceration period. Stir gently to combine all ingredients thoroughly.
Return the mixture to the refrigerator for another 24-48 hours, stirring occasionally. This resting time allows the flavors to meld and develop complexity.
Strain the mixture through a fine-mesh sieve lined with cheesecloth into a clean bowl, pressing gently on the solids to extract maximum flavor. Discard the solids.
Transfer the finished shrub to a clean glass bottle or jar with a tight-fitting lid. Store in the refrigerator for up to 6 months, noting that the flavors will continue to develop and mellow over time.