In a bowl, combine chocolate chips and ½ cup of heavy cream. Heat in the microwave in 30 second increments, whisking in between increments until the chocolate is fully melted. Set aside and cool completely.

While the chocolate is cooling, combine the rest of the heavy cream, powdered sugar, and vanilla in a stand mixer and whip until stiff peaks form.

Remove half of the whipped cream and set aside in a bowl. Carefully fold the cooled chocolate mixture into the remaining whipped cream until combined.

Assemble the trifle by layering the bag of the chocolate chip cookies, then half of the whipped cream, another bag of the chocolate chip cookies, the chocolate mousse, a final bag of the chocolate chip cookies, and then the remaining whipped cream. Garnish with snowman cookies and rosemary, if desired. Chill until ready to serve.