Add 5ml powdered sugar and 60ml carbonated water to a collins glass and stir until the sugar fully dissolves.
Fill the glass with ice.
Add 60ml gin and 30ml dry vermouth and stir gently to combine.
Top with an additional 60ml carbonated water and stir once more, gently.
Garnish by placing a lemon peel twist inside the glass and draping a long orange spiral over the rim.
Dissolving the sugar in a small measure of soda water before adding ice ensures even sweetness throughout the drink without the grittiness of undissolved sugar. The dual citrus garnish - lemon peel inside, orange spiral over the rim - is classic cooler presentation and contributes meaningful aromatic oils with every sip.
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