1. In a medium-sized saucepan boil the milk with cream and coffee.
2. Mix the egg yolks, sugar, and cornstarch in a bowl.
3. Pour the hot milk mixture over the egg yolks, mix well, and return to the saucepan, stirring constantly, until the mixture thickens slightly.
4. Strain the hot mixture and pour it onto the chopped chocolate, and use an immersion blender to create a smooth cream.
5. Allow the mousse to cool slightly, then pour it into a 10-inch pan (or three six-inch round rings, used as above, with an additional parchment paper strip along the inside of the ring to make it easier to remove later), or silicone molds that are the same size as the rings used to prepare the crunch base, and transfer to the freezer for four hours.
6. Release and place on the prepared crunch.