With a food processor or in a large zip-topped bag with a rolling pin, crush the chocolate sandwich cookies to crumbs.
Place the chocolate and ¼ cup heavy cream in a bowl. Set over pot of simmering water and melt until smooth, stirring often. (This can also be done in a double boilder.) Set aside to cool to room temperature.
Beat remaining heavy cream to soft peaks. Gently fold the whipped cream into the chocolate in 2-3 additions, gently folding each addition in until no streaks of chocolate remain.
Layer the Oreo crumbs and chocolate into 4 glasses. Top with more whipped cream and a cookie, if desired.
Serve immediately or store in the fridge for up to 24 hours.