Make the graham cracker crust. Line an 8"x8" square baking pan by coating with butter and lining with parchment paper.
Add graham crackers to a food processor or plastic bag and crush into fine crumbs. Add crumbs to a medium-sized bowl, then stir in melted butter, sugar, and salt.
Add the crumb mixture into prepared pan and press into a compact, even layer on the bottom. Chill in the freezer while you make the mousse.
Make the Chocolate Mousse. Add the chocolate to a medium-sized bowl. Add ¾ cup of heavy cream, instant coffee, and salt to a saucepan. Heat until very hot, but not boiling, stirring as needed.
Pour the hot cream over the chocolate and let sit for about 5 minutes. Add vanilla extract and stir until smooth and a ganache is created. Set aside to cool completely, adding to the fridge to speed up the process if needed.
In a large bowl, add the remaining ¾ cup of heavy whipping cream. Beat with an electric mixer until stiff peaks form. Fold the chocolate ganache into the whipped cream until combined.
Add the mousse to the prepared crust, spreading into an even layer. Cover with plastic wrap and chill in refrigerator until firm, at least 2 hours.
Cut into squares and top with whipped cream to serve. Enjoy!
Store chocolate mousse bars in an airtight container in the refrigerator for up to 4 days.You can easily make the chocolate mousse recipe without the crust. Simply add to individual glasses or in your dish of choice before chilling.