TO MAKE THE CRANBERRY-CHERRY COULIS In a 272-quart saucepan, combine the cherries, cranberries, sugar, and lemon juice.
Bring to a simmer over medium heat.
Reduce the heat if the berries start to splatter, and cook until the cranberries pop, about 10 minutes.
Set aside to cool for 20 minutes.
Transfer to the work bowl of a food processor and puree.
Chill while making the chocolate mousse.