1. Rub rim of a chilled margarita glass with lime wedge, and dip rim in salt to coat, if desired.
2. Combine lime juice, liqueur, tequila, and powdered sugar in a small pitcher or measuring cup; stir until powdered sugar is dissolved. Pour into a zip-top plastic freezer bag. Seal and freeze 8 hours. Let stand 5 minutes at room temperature before serving. Pour into prepared glass.
*1/3 cup thawed frozen limeade concentrate may be substituted for fresh lime juice. Omit powdered sugar, and proceed with recipe as directed.
Note: For testing purposes only, we used Cointreau for orange liqueur and Jose Cuervo Especial for tequila.