In a pitcher, muddle the blackberries along with 1/4 cup Simple Syrup. Stir in the gin and lemon juice. Taste and add simple syrup as needed. Refrigerate for at least 30 minutes before straining.
Fill 4 to 6 shot glasses with crushed ice. Top off with the blackberry mixture and garnish with the reserved blackberries. Serve immediately.
Combine the sugar with 1 cup water in a small saucepan and bring to a boil over medium heat. Boil until the sugar is dissolved. Let cool. Transfer to a container and refrigerate, covered, for up to 1 month.