Line a 9 by 13 inch baking pan with parchment paper, leaving a 2 inch overhang on the two longer sides.

In a food processor, pulse the almonds until finely chopped. Add the Oreos and pulse until Oreos and almonds are crumbs. Turn almond-Oreo mixture out into a medium sized bowl and stir with butter until all the crumbs are well coated with butter. Press mixture into the bottom of the prepared pan. Make sure to pack the crumbs in well. Place crust in the freezer. 

Add the chopped chocolate or chocolate chips to a medium sized heat proof bowl. 

In a small saucepan, heat 1 cup of heavy cream with the salt til very hot but not boiling.

Pour hot cream over the chocolate. Push chocolate down into the heavy cream if needed. Allow to sit 2 minutes. Add the vanilla extract. Stir until chocolate has melted and mixture is smooth. Allow to cool completely. 

Once the chocolate mixture has cooled, pour 2 cups of cold heavy cream in the bowl of an electric mixer fitted with the whisk attachment. Whip the heavy cream to stiff peaks.Add the cooled chocolate mixture and gently fold to combine. Pour the mixture over the chilled crust. Use an offset spatula, a spatula or the back of a spoon to spread evenly. 

In the bowl of an electric mixer fitted with the whisk attachment or in a large bowl using a hand held mixer, add the heavy cream, powdered sugar, vanilla extract and salt. Beat on low for 40 seconds. Increase speed to medium and beat another minute or until you reach stiff peaks. Spoon whipped cream over the chocolate mousse layer and spread evenly. Top with chopped Oreos and almonds, if desired. Cover with plastic wrap and place in the refrigerator for at least 3 hours or overnight, until mousse is firm and set. When ready to serve, slice with a sharp knife. Store leftover chocolate mousse bars in an airtight container in the refrigerator for up to 4 days.