Combine the prunes, water, ½ cup orange juice, sugar or honey, and orange zest in a small saucepan over medium heat. Bring to a boil, reduce the heat to low, and cook until the sauce thickens, about 20 minutes. If the mixture is too sweet, add a bit of lemon juice or more orange juice for balance, then add a nice grinding of black pepper.
Let cool, cover, and store in the refrigerator for up to 3 months. Bring to room temperature, before serving. Serve with robiola cheese.