Typically made from rolled sponge cakes, festive yule logs can be tricky for an inexperienced baker. Our ice box version, made by sandwiching chocolate wafer cookies with whipped cream, couldn’t be easier to prepare.
Beat the heavy cream and confectioners’ sugar in a large bowl with a mixer on medium-high speed until stiff peaks form, about 3 minutes. Beat in the peppermint extract. (Do not overbeat.)
Spread a thin 3-by-8-inch rectangle of whipped cream on a board or platter. Sandwich 2 cookies together with about 1 teaspoon whipped cream; stand the cookies upright (on their edges) at one end of the whipped cream rectangle and continue adding cream and cookies to form an 8-inch log (you should use about 36 cookies).
Sandwich 2 more cookies together with about 1 teaspoon whipped cream; use whipped cream to attach the cookies to the side of the log on an angle. Continue attaching about 8 more cookies to make the branch.
Cover the log and branch with the remaining whipped cream. Using an offset spatula, make long lines in the whipped cream to look like bark. Mix the cocoa powder and 1 tablespoon warm water in a bowl; add a few more drops warm water as needed until the mixture is brushable. Using a small pastry brush, paint short lines of the cocoa mixture on the whipped cream to look like birch bark. Paint spirals at the end of the log and branch.
Refrigerate the cake until the whipped cream is set, about 1 hour. Cover loosely with plastic wrap and continue refrigerating until the cookies are soft, at least 6 hours or overnight. Slice on an angle.