Step 1: Prepare the Cookie Base

1. Place the chocolate cookies in a zip-top bag and crush them using a rolling pin until you have fine crumbs.
2. Transfer the crumbs to a bowl and pour in the melted butter.
3. Mix until the crumbs are evenly moistened.
4. Set aside while you prepare the other layers.

Step 2: Make the Chocolate Mousse

1. Place the chopped chocolate in a medium heatproof bowl.
2. In a small saucepan, heat 1/2 cup of heavy cream until it just begins to simmer (do not boil).
3. Pour the hot cream over the chocolate and let it sit for 1 minute.
4. Gently stir until the chocolate is completely melted and the mixture is smooth.
5. Stir in the vanilla extract and a pinch of salt.
6. Allow the mixture to cool to room temperature, about 10-15 minutes.

Step 3: Whip the Cream for Mousse

1. In a large mixing bowl, use an electric mixer to whip the remaining 1 1/2 cups of heavy cream with the granulated sugar until stiff peaks form.
2. Check that your chocolate mixture has cooled (it should feel barely warm to the touch).
3. Using a spatula, gently fold one-third of the whipped cream into the chocolate mixture to lighten it.
4. Gradually fold in the remaining whipped cream until no streaks remain. Be careful not to deflate the mixture.

Step 4: Prepare the Whipped Cream Layer

1. In a clean mixing bowl, combine 1 cup heavy cream, powdered sugar, and vanilla extract.
2. Whip on medium-high speed until soft peaks form.
3. Transfer to a piping bag fitted with a star tip if desired, or keep in a bowl for spooning.

Step 5: Assemble the Parfaits

1. Take 4-6 clear glasses or parfait cups (8-10 oz size works well).
2. Add a layer of cookie crumbs to the bottom of each glass (about 1-2 tablespoons).
3. Gently spoon or pipe a layer of chocolate mousse over the cookie crumbs.
4. Add another thin layer of cookie crumbs.
5. Add another layer of chocolate mousse.
6. Top with a generous swirl or dollop of whipped cream.
7. Finish with a sprinkle of cookie crumbs, chocolate shavings, or fresh berries.

Step 6: Chill and Serve

1. Refrigerate the parfaits for at least 1 hour (or up to 24 hours) before serving.
2. Just before serving, add any final garnishes that might soften in the refrigerator (like mint leaves).