Prep: 5 minutes; Freeze: 1 hour or more; Total time: About 1 hour, 35 minutes.A little bit of vodka makes the fro-yo easier to scoop, thanks to its alcohol content and ultra-low freezing point.
In a large bowl, stir together yogurt, 3/4 cup sugar, and vodka until sugar dissolves. Pour into the freezer can of an ice-cream maker; freeze according to manufacturer's instructions.
In a medium bowl, mash together raspberries and remaining 1/4 cup sugar. Swirl mixture into frozen yogurt; spoon yogurt into a metal loaf pan. Cover and freeze for 1 hour, or until firm. To serve, leave yogurt at room temperature to soften slightly before scooping.