Preheat the broiler.
Remove some of the grapefruit peel for a twist garnish, then cut the grapefruit in half. Place the grapefruit halves on a baking sheet flesh-side up and sprinkle the sugar evenly over the tops. Place under the broiler until the sugar is caramelized, about 6 minutes.
Meanwhile, fill a highball glass with ice and add the vodka. Remove the toasty grapefruit and squeeze the juice into the glass. Top with the ginger ale and garnish with the grapefruit twist.
Recipe courtesy of Trisha Yearwood