Prepare the base:

• In a food processor, pulse the Nilla wafers until finely ground; add the sugar and butter and pulse several times until well mixed and the crumbs are evenly moistened.
• Alternatively: Place cookies in a large, heavy ziploc bag. With a rolling pin (or other heavy object), crush the cookies. Add the sugar and butter, and shake and massage until the crumbs are evenly moistened.
• Another option: Crush the cookies in a blender; don’t mix in the sugar and butter in the blender (it’s too hard to remove), but instead add the crumbs to a bowl and mix the sugar and butter in by hand.

Place the crumbs in the bottom of an 8×8″ pan lined with parchment paper (for easy removal), and press into an even layer. (A dry measuring cup works well for this, but pay attention to the corners.)

Freeze the crust for 15 minutes.

Make the Filling:

Once the crust has been in the freezer for about 12 minutes, add a teaspoon of vanilla to the cream if using. In a large bowl, add the pudding. Pour about 1/3 of the cream in, beating on low with an electric beater. While still beating, slowly pour in the remainder of the cream until the mixture has thickened. This process takes about 1 1/2 minutes.

Spread the pudding mixture over the chilled crust layer in an even layer. Place in the refrigerator for at least 10 to 15 minutes before adding ganache.

Prepare the ganache:

Place the chocolate chips in a heatproof bowl. Bring the cream to just a simmer (small bubbles around the edge of the pan). Do not boil.

Immediately pour the hot cream over the chocolate chips. Allow to sit for a minute, then gently whisk the chocolate and cream together until smooth.

Allow the ganache to cool and thicken for about 3 minutes for a smooth topping, or around 5 minutes to make decorative swoops.

Chill for at least 2 hours before serving; overnight will give cleaner cuts. Refrigerate for up to three days, tightly covered.