Step 1In a bowl, sprinkle the gelatin over the cold water and set aside to give the gelatin time to absorb the water, about 2 minutes. Add the boiling water and stir until the gelatin is fully dissolved. Add the sugar and orange extract and stir until the sugar is dissolved. Refrigerate the mixture until thickened. Arrange the mandarin orange slices on the bottom of a 6-cup mold and gently spoon the clear gelatin into the mold over the orange slices. Refrigerate until the gelatin is set but not firm.
Step 1To make the second layer, in a large saucepan, whisk together the milk, cocoa, sugar, orange extract and orange zest. Bring just to a boil over medium heat, careful not to let the milk mixture boil over. Remove from heat and set aside.
Step 2In a separate bowl, sprinkle the gelatin evenly over the cold water and set aside to give the gelatin time to absorb the water, about 2 minutes. Add the hot milk mixture and stir until the gelatin is fully dissolved. Set the mixture aside until cooled to room temperature, then gently spoon into the mold over the mandarin orange layer. Refrigerate until firm. Unmold and serve.