Zest one lemon lightly (optional) and then roll lemons and limes on the counter to loosen juices. Halve and juice enough lemons to yield 0.75 cups (6 fl oz) fresh lemon juice and enough limes to yield 0.25 cups (2 fl oz) fresh lime juice. Strain through a fine mesh into a measuring cup to remove pips and pulp.

Combine base ingredients

In a large mixing pitcher or cocktail shaker big enough for multiple servings, pour in 0.75 cups fresh lemon juice, 0.25 cups fresh lime juice, 0.5 cups simple syrup, 2 cups gin, 0.25 cups dry vermouth, and 0.25 cups orange curaçao. Stir gently to combine.

Chill and aerate

Add 6 cups of cubed ice to the shaker or pitcher, cap or cover, and shake vigorously for 10–15 seconds (or, if using a pitcher, stir briskly for 20–30 seconds) until the exterior is frosty and the mixture is well chilled and slightly diluted.

Carbonation & Finish

Prepare glassware

Fill eight rocks or highball glasses halfway with fresh ice (reserve extra cubes if you prefer more dilution). If serving in a shared pitcher, pre-chill the pitcher and glasses in the freezer for 10 minutes for best results.

Top with soda and bitters

Strain the chilled gin-citrus mixture evenly into the prepared glasses (or pour into the chilled pitcher). Divide 2 cups chilled club soda among the glasses (about 1/4 cup or 2 fl oz per glass) and add a few drops of Angostura bitters to each glass (roughly 1–2 dashes per serving; total used above equals 10 tsp—distribute as desired). Gently stir once to incorporate carbonation without flattening it.

Garnish and serve

Gently slap a mint sprig between your hands to release aroma and tuck it into each glass along with a lemon wheel on the rim. Optionally express an extra lemon peel over each drink for bright oils. Serve immediately while fizzy.