To make the whipped cream, place heavy cream, confectioners sugar and vanilla in a bowl of a stand mixer fitted with a whisk attachment or in a bowl with a handheld electric mixer.
Beat on medium speed until thick and fluffy, like whipped cream. Set in the fridge meanwhile.
To prepare the ganache, begin with boiling the heavy cream in a small saucepan. Then, pour over a bowl of chocolate chips. Allow to sit for 3 minutes, then stir together until a thick chocolate mixture forms. Cover the bowl with plastic wrap, pressing directly onto the ganache, and allow it to sit in a cool place on the counter overnight.
For the Chocolate Covered Oreo “Eyes”, place white chocolate with vegetable shortening in a microwave safe bowl. Microwave for 20 second intervals, stirring in between, until fully melted. Dip each Oreo into the melted chocolate and allow excess chocolate to drip off before placing onto a parchment lined baking sheet to dry. Place ganache into a ziplock bag and snip off the corner and pipe a dot in the top right corner of each oreo to create the eyeball effect. Use a toothpick to smooth the ganache into a circle shape if needed.
To assemble the Cookie Monster cake, level each cake using a serrated knife.
Place a cake board onto a cake turn-table or your counter and spread a bit of whipped cream onto the center to help your cake stick. Place the first layer of cake, cut side down, onto the cake board.
Spread the whipped cream onto the first cake layer and sprinkle with crushed cookies (be sure to save some whole cookies for the cake decorations).
Place the second cake layer on top and press down. Run an offset spatula around the sides of the cake to smooth out any whipped cream that oozed out of the cake.
Ice the entire cake in chocolate ganache. This layer does not have to be gorgeous because nobody will see it, but it should be smooth for piping onto.
Fill a piping bag with the teal colored Buttercream, fitted with a coupler and tip #233 (Wilton grass tip) and pipe grass all around the sides and top of the cake.
Place the chocolate covered Oreo eyes onto the top-center of the cake.
Then, arrange the cookies around the mouth area of your cookie monster cake. I broke the bottoms off of many of the cookies so that they weren't too high. You can also place a few broken cookie pieces on the sides and bottom of the cake to make it seem like Cookie Monster overstuffed his face and food is falling out.