For the Mousse: In a small saucepan over medium heat stir together the milk with the sugar and the espresso powder until the milk is hot, but not boiling, and the sugar is dissolved. Place the chocolate chips in a blender. Pour the hot milk over the chips. Run the blender on high until combined, a few seconds. Add the egg whites and run the blender on high until light, about 1 minute. Transfer the mousse to 4 small serving cups. Cover with plastic wrap and place in the refrigerator until firm, about 3 hours.
For the Cream: In the bowl of an electric mixer, stir together the mascarpone cheese and the orange juice until smooth. Add the cream, powdered sugar, and orange zest. Whip until the cream has soft peaks, about 1 minute. Whip the cream just before serving the mousse or cover with plastic wrap and place in the refrigerator until ready to serve. When blending hot liquids: Remove liquid from the heat and allow to cool for at least 5 minutes. Transfer liquid to a blender or food processor and fill it no more than halfway. If using a blender, release one corner of the lid. This prevents the vacuum effect that creates heat explosions. Place a towel over the top of the machine, pulse a few times then process on high speed until smooth.