Crush the oreos (the whole cookie with the cream) either by chopping with a knife, lightly blending in a blender or crushing with a rolling pin. Set aside.

In a small pot over low heat on the stove, heat 1/3 cup heavy cream just until boiling. Place the white chocolate chips in a bowl. Once the cream is bubbling, remove from the heat and pour it over the white chocolate chips. Allow the chips to sit for 1 minute. Then use a spatula to mix until the chips are smooth and completely melted. Allow the melted chocolate to cool to room temperature.

Pour the remaining 1 & 2/3 cups heavy cream into the chilled bowl and beat on high with an electric mixer until stiff peaks form, this will take 3-5 minutes. 

Add the cooled white chocolate and crushed oreos to the whipped cream and beat until the mixture is fully combined. 

Divide the mousse into individual serving containers. Cover the containers with plastic wrap and refrigerate at least 3 hours. I frequently refrigerate the mousse overnight, so longer is fine. The mousse will keep for 2-3 days in the fridge.

Before serving make the whipped cream topping if desired. In a chilled bowl combine 1/2 cup heavy cream and powdered sugar, beat on high with an electric mixer until stiff peaks form, this will take 2-3 minutes. Top the mousse with a dollop of whipped cream. Serve. Cover leftovers with plastic wrap and refrigerate.