Heat milk over medium-high heat in a small heavy saucepan to 180° or until tiny bubbles form around edge (do not boil). Remove from heat. Add rind and cinnamon; cover and let stand 30 minutes. Discard rind and cinnamon.
Combine 1/4 cup sugar, cornstarch, and salt in a small bowl, stirring well with a whisk. Add 1/4 cup milk to sugar mixture, stirring until smooth. Return milk mixture to pan; cook over medium-low heat 7 minutes or until almost thick, stirring constantly with a whisk. Place egg yolks in a small bowl. Gradually pour one-third of hot milk mixture into yolks, stirring constantly with a whisk. Carefully return yolk mixture to pan. Cook over low heat 4 minutes or until a thermometer registers 180°, stirring constantly with a whisk. Divide custard evenly among 6 (4-ounce) custard cups; press plastic wrap against surface of custard. Chill at least 4 hours.
Remove plastic; discard. Sprinkle remaining 3 tablespoons sugar evenly over custards. Holding a kitchen blowtorch about 2 inches from the top of each custard, heat the sugar, moving the torch back and forth, until sugar is completely melted and caramelized (about 1 minute). Serve immediately or within 1 hour.