Frozen Palomas

Combine the grapefruit juice, tequila, lime juice and ¹⁄₄ cup of simple syrup in a quart container and freeze it for at least 6 hours or overnight, until solid. Break up the mixture with a fork and transfer half of it to the jar of a blender. Add ¹⁄₈ tsp salt and blend until smooth. Divide the frozen mixture between two highball glasses, then repeat with the rest of the frozen mixture. Garnish with a grapefruit wedge.