Start by making a simple syrup: dissolve the sugar in the water in a medium saucepan. Add vanilla beans and bring to a simmer. Add the orange juice and cranberries, a dash of salt and some freshly ground black pepper, to taste. Simmer until cranberries begin to pop and become tender, about 3 to 5 minutes. Remove from heat and stir in Dijon mustard. Chill cranberry sauce until ready to serve. The sauce can be made up to 2 days ahead of time. Just before serving, garnish sauce with freshly grated orange zest.