Add 1 cup heavy cream to a saucepan over medium heat. Bring to a simmer.Pour white chocolate chips into a mixing bowl. Pour simmering cream over the top, and stir until melted and smooth. Set aside to cool.
Add remaining 1 cup of cream to a large mixing bowl and beat until stiff peaks.
Fold into the cooled white chocolate mixture, along with 1/2 cup of the crushed candy. Cover with plastic wrap, and refrigerate for 3-4 hours.
Make the chocolate pudding and set aside.
Make the brownies and allow to cool completely. Cut into small squares.
To assemble:
Cover the bottom of your serving cups (or a large trifle dish) with brownie pieces. Add spoonfuls of pudding on top.
Smooth a layer of mousse on top of the pudding. Repeat with 2 more layers.
Cover with plastic wrap until ready to serve. Garnish with crushed peppermint candies just before serving.
Notes
I've found it easiest to make the mousse and the pudding (steps 1-3) a day or two in advance, to save time.