Add 5–6 fresh blackberries to an old-fashioned glass and muddle firmly until well crushed.
Fill the glass with crushed ice.
Combine gin, fresh lemon juice, and simple syrup in a cocktail shaker with ice.
Shake well for 10–12 seconds until fully chilled.
Strain the shaken mixture over the crushed ice and muddled blackberries in the glass.
Top with soda water and stir gently once to incorporate.
Garnish with 3–4 fresh blackberries and 2–3 sprigs of fresh mint. Serve immediately.
For maximum blackberry flavour and a striking deep-purple colour bleeding through the crushed ice, muddle the berries directly in the glass before building the drink rather than in the shaker - this keeps the fruit texture visible and lets the colour streak naturally as the cocktail is sipped.
My Bar Shelf reads your shelf and shows you every cocktail you can make from what you already own, including Mountain Bramble.