Whisk the water and sugar together in a medium saucepan. Add the orange juice, rind and pulp. Stir to combine. Cook over very low heat until the mixture starts to boil. Boil for 2-3 minutes and remove from heat. Cool completely and then add the Grand Mariner and buttermilk. Refrigerate the sorbet mixture overnight. Process according to your ice-cream maker instructions. Freeze until ready to serve. Allow the sorbet to sit for 10 minutes to soften before serving.
Notes
(Adapted from a recipe by The Endless Meal)Nutrition information is calculated using an ingredient database and should be considered an estimate. When multiple ingredient alternatives are given, the first listed is calculated for nutrition. Garnishes and optional ingredients are not included.