The Bitter End Recipe

1. Juice and sweeten

Roll the grapefruit and lemon on the countertop to loosen juices. Cut and juice enough grapefruit to yield 3 oz (about half a medium grapefruit) and juice the lemon to yield 0.5 oz (about half a lemon). Measure the juices into a cocktail shaker or mixing glass. Add 0.5 oz chilled simple syrup (1:1).

2. If you prefer a smoother, less pulpy mocktail, strain the combined juices and syrup through a fine-mesh strainer into the shaker or mixing glass to remove membranes and seeds.

3. Mix and build

Fill a Collins or highball glass with ice (or if using a shaker, add ice to the shaker). Pour the measured grapefruit-lemon-syrup mixture over the ice in the glass. Top gently with 3 oz tonic water, pouring slowly to preserve carbonation. Stir once or twice gently with a bar spoon to combine — avoid vigorous stirring to keep tonic bubbly.

4. Garnish and serve

Express the oils of a grapefruit twist over the drink by holding the twist skin-side down above the glass and giving it a quick snap, then rub the rim with the peel and drop it in, or rest a grapefruit wedge on the rim. Serve immediately with a straw or stirrer.