Combine 1 cup frozen blackberries, water and sugar in a medium-sized saucepan over medium-high heat. Bring to a boil.

Remove from heat when sugar has dissolved completely then set aside to cool.

Once cooled, strain through a sieve, discarding the pulp and seeds. This should yield about 1½ cups of blackberry simple syrup.

Pour into cocktail shaker with brandy and Cointreau, shake with cracked ice. Strain into chilled glass packed with ice then drop in lemon twist.