Zest the oranges and set the zest aside. Cut the oranges in half and juice them into the jar of a blender--you should have about 1/3 cup of juice (you can supplement it with another orange, some store-bought juice, or a little water if necessary.)

Add the vinegar, honey, mustard, salt, and pepper to the jar of the blender. While blender is running on low speed, add the oil in a slow, steady stream. Transfer to a storage container and stir in the reserved zest. Allow to stand for at least 1 hour before serving.