In a large bowl, whip the heavy cream to glossy, medium-hard peaks, about 5 minutes. Set aside in the fridge. In a small saucepan over gentle heat, melt the sugar with ¼ cup water until dissolved. As soon as the syrup begins to boil, turn off the heat. 

Add chocolate and eggs to a blender. Blend on medium-high speed while slowly pouring in the hot sugar syrup, which will melt the chocolate and cook the eggs. Keep the machine running until the mixture is extremely smooth, then stream in the espresso, Drizzle, vanilla, and salt. Keep blending until the mixture has cooled to room temperature, about 1 minute, pausing to scrape the sides as needed. 

Fold 1 cup of the chocolate mixture into the chilled whipped cream until smooth, then add the rest of the chocolate mixture to the cream mixture and fold until there are no steaks. Pour into the individual bowls, ramekins or glasses, and set in the fridge until firm, at least 2 hours or up to 24 hours. Serve chilled. 

While mousse is setting, make the whipped topping by whipping cream in a medium bowl until medium peaks form. Add powdered sugar and Drizzle and mix until fully incorporated. Store in the fridge until serving. 

Once mousse has set, serve with the whipped topping, flaky salt, more Drizzle, and orange zest. Enjoy!