In top of a double boiler or a metal bowl over simmering water whisk egg yolks and sugar until blended. Stir in liqueur, water, orange juice and zest. Cook over low heat until mixture is just thick enough to coat a metal spoon and a thermometer reads at least 160°, about 10 minutes, stirring constantly but gently. Do not allow to boil. Immediately transfer to a bowl.
Place bowl in an ice-water bath for a few minutes, stirring custard occasionally. Cool to room temperature. In a large bowl, beat cream until it begins to thicken. Add confectioners' sugar; beat until stiff peaks form. Gently fold into cooled custard mixture.
Transfer to eight 4-oz. ramekins; smooth tops. Freeze until firm, at least 4 hours or overnight. Garnish with additional orange zest.