In a medium saucepan, combine the fresh heavy cream and sugar. Heat over medium heat, stirring occasionally, until the sugar has dissolved completely and the mixture is just about to boil.
Once the cream is heated, remove it from the heat. Stir in the zest of 1 orange, orange juice, and lemon juice. The mixture will begin to thicken as it cools.
If you prefer a smoother texture, pour the mixture through a fine mesh sieve into a large bowl or individual ramekins.
Let the Orange Posset cool to room temperature, then cover them with plastic wrap and refrigerate for at least 4 hours, or until set.
Once set, serve the Orange Posset chilled. You can garnish with fresh fruit, whipped cream, or a drizzle of white chocolate raspberry mousse cups.