Pour the guava juice into an ice cube tray and freeze overnight. (One cup of juice should make 8 standard ice cubes.)
Rub a lime wedge around the edge of a margarita glass and dip immediately in the margarita salt, turning to coat. Place the glass in the freezer for 10 minutes.
In a blender, combine the lime juice, tequila, Triple Sec, simple syrup, and guava ice cubes and pulse until smooth. Pour into the prepared glass, garnish with a lime wedge, and serve immediately.
Yield: 1 serving