Combine blackberries, sugar and water in a small saucepan over medium heat. Stir occasionally, smashing berries with the back of a spoon, until sugar dissolves and mixture simmers, about 6–8 minutes.

Remove from heat, add lemon zest if using, and let cool 10 minutes. Press mixture through a fine-mesh strainer into a jar, using the back of a spoon to extract as much juice as possible. Discard solids. Let syrup cool completely before using. Refrigerate up to 2 weeks.

Cocktail Assembly

Dry shake (if using egg white)

Add bourbon, lemon juice, blackberry syrup, ginger liqueur, bitters and egg white to a cocktail shaker (no ice). Dry shake vigorously for 15–20 seconds to emulsify and create foam.

Wet shake

Add a generous handful of ice to the shaker and shake hard for 10–15 seconds until chilled and slightly diluted.

Strain the cocktail through a fine mesh strainer into a chilled rocks glass over one large ice cube (or into a coupe if you prefer without large cube). The fine strain removes any small berry seeds or ice shards and ensures a silky texture.

Garnish: thread two fresh blackberries on a toothpick and rest across the glass, then express a lemon twist over the drink and drop or rest on the rim.

Serve immediately. Sip to enjoy the interplay of warm bourbon, tart blackberry, bright lemon and spicy ginger notes — the 'Iron Horse Station' is a balanced modern craft cocktail.