This seriously easy and decadent mousse hides a smart secret: reduced-sodium soy sauce. Just 1/2 teaspoon elevates the rich dark chocolate flavor. Add crunch with cookies to contrast the mousse's silky texture. Heating store-bought shortbread in the oven opens up the flavors of the buttery cookies.
Microwave chocolate in a large microwave-safe bowl at HIGH 1 minute or until slightly melted.
Bring coffee, next 3 ingredients, and 2/3 cup cream to a simmer in a small saucepan over medium heat. Pour cream mixture over chocolate in bowl. Let stand 15 seconds, and stir until smooth. Cool completely (about 30 minutes).
Beat remaining 1 cup cream at high speed with a heavy-duty electric stand mixer, using a whisk attachment, until foamy; gradually add sugar, beating until soft peaks form. Stir in 1/2 cup coffee mixture until blended; gradually fold in remaining coffee mixture. (Mixture will be loose.)
Spoon chocolate mixture into a shallow 2-qt. bowl or 6 (8- to 10-oz.) glasses. Cover with plastic wrap (without touching mousse), and chill 2 to 3 hours. Serve with cookies, if desired, and toppings.
Note: We tested with Walkers Pure Butter Assorted Shortbread cookies. Warm shortbread in the oven at 350° for 5 minutes so they taste freshly baked.
Make-Ahead Tip: Refrigerate mousse, without desired toppings, up to 2 days.