Preheat oven to 350°F. Spray the bottom of a 9x13 baking dish with baker's spray.
Combine the brownie mix, eggs, water, and vegetable oil in a large mixing bowl. Whisk to combine according to package directions.
Pour the brownie batter into the prepared baking dish and bake for 25-30 minutes or until a toothpick inserted into the center comes out clean. Allow the brownies to cool completely at room temperature before adding the French silk layer.
To make the French silk layer, add the chopped semi-sweet chocolate baking bar and unsalted butter to a medium, microwave-safe bowl, and melt the chocolate at 50% power for 1 minute. Stir and heat at 50% for an additional 30 seconds and stir again. Repeat in 30-second intervals at 50% power until your chocolate is melted. Stir the melted semi-sweet chocolate until completely smooth. Set aside.
In a large mixing bowl, beat the room-temperature cream cheese, using a handheld mixer on medium speed, for 1-2 minutes or until light and fluffy.
Add the powdered sugar to the bowl of cream cheese, one cup at a time, and beat on low speed until fully incorporated and no lumps remain.
Add the vanilla extract and the melted semi-sweet chocolate to the cream cheese mixture. Beat on low speed until the chocolate is fully incorporated and the mixture begins to get light and fluffy.
Fold the thawed whipped topping into the French silk mixture using a large rubber spatula until no white streaks remain.
Using an offset spatula, spread the French silk mixture evenly over the surface of the cooled brownies.
Chill the French silk brownies for 1-2 hours to allow the French silk mixture to firm up before slicing and serving.
You can add the optional garnishes to single servings if desired. A dollop of whipped topping, followed by a sprinkle of chocolate shavings and a drizzle of chocolate sauce.
Ensure the cream cheese, butter, and whipped topping are at room temperature for easy mixing.
Be sure to follow the directions on the back of the box of brownie mix for the brand you purchased. You may note that the proportions of oil, water & eggs may differ from the brand used in this recipe. If you use a glass dish, you may need to add an additional couple of minutes to your baking time from what your box suggests. Be sure to follow the directions for fudge-like, not cake-like, brownies for this recipe.
Oven temperatures vary and may need to be recalibrated periodically to ensure they are accurate. Make sure to check your brownies at the lower end of the recommended baking time.
When melting your chocolate and butter in the microwave, you will need to note that the microwave used for this recipe is 1000 watts. Your microwave may take longer or less time to melt your chocolate. You just want to keep an eye on it so that you do not burn the chocolate.
To garnish my single servings of these French silk brownies, I like to place the additional thawed whipped topping into a large piping bag fitted with a large decorative piping tip and pipe on a decorative dollop of the whipped topping on top of the brownies.