Combine sherry and shallot in a medium saucepan. Cook over medium-high heat about 4 minutes or until reduced to 2 tablespoons.
Meanwhile, combine mangoes, orange juice, and vinegar in a blender. Process until smooth. Add pureed mango mixture to sherry reduction, and reduce heat to medium.
Cook 3 to 5 minutes or until mixture is slightly thickened. Remove from heat. Whisk in butter, 1 piece at a time, until thoroughly blended. Stir in salt and pepper.