Line a 9x13-inch pan with parchment for easy lifting. Set aside a handful of graham crackers for trimming to fit gaps.
Make the peppermint cream: Beat the cream cheese on medium-high until velvety and no lumps remain, 1–2 minutes. Add powdered sugar, heavy cream, peppermint extract, and the optional vanilla; beat until light and fluffy.
Fold in 8 oz (about 3 cups) of Cool Whip and 1 cup of the Andes Peppermint Chips; reserve the remaining 1/4 cup chips for layering. Chill this cream mixture for 10 minutes to slightly firm up.
Prepare the pudding: Whisk the dark chocolate pudding mix with the cold milk for 2 minutes. Let stand 5–8 minutes until thickened yet spreadable.
Anchor the first layer: Spread a very thin swipe of the peppermint cream in the bottom of the pan so the crackers don’t slide. Arrange a tight layer of chocolate graham crackers, trimming to fit as needed.
Spread half of the peppermint cream evenly over the crackers. Sprinkle 1–2 tablespoons of the reserved peppermint chips over this layer for extra crunch.
Gently spoon on half of the pudding and smooth to the edges. Tap the pan once or twice to settle the layers.
Add a second graham layer, turning the crackers the opposite direction. Top with the remaining peppermint cream, then the remaining pudding, smoothing each layer before adding the next.
Finish with the remaining 8 oz Cool Whip, swirling it across the surface. Cover and refrigerate at least 4 hours, preferably overnight, until the crackers have softened and the layers slice cleanly.
Right before serving, drizzle with warm dark chocolate sauce and shower with additional Andes Peppermint Chips. For ultra-neat squares, freeze the pan for 10–15 minutes and cut with a hot, dry knife.