Creating French Silk Brownies is straightforward if you follow these easy steps:

1. Preheat the Oven: Set your oven to 350°F (175°C). Grease a 9×13-inch baking pan or line it with parchment paper for easy removal.
2. Melt Butter: In a medium saucepan, melt 1 cup of unsalted butter over low heat.
3. Mix Sugar and Butter: Once melted, remove from heat and stir in 2 cups of granulated sugar until well combined.
4. Add Eggs: Mix in 4 large eggs, one at a time, ensuring each is fully incorporated before adding the next. Stir in 1 teaspoon of vanilla extract.
5. Combine Dry Ingredients: In a separate bowl, sift together 1 cup of all-purpose flour, 1 cup of unsweetened cocoa powder, and 1/2 teaspoon of salt.
6. Combine Mixtures: Gradually add the dry mixture to the wet mixture, stirring until just combined.
7. Pour Batter: Pour the brownie batter into the prepared baking pan, spreading it evenly.
8. Bake: Bake in the preheated oven for 30-35 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs.
9. Cool the Brownies: Remove from the oven and allow the brownies to cool completely in the pan.
10. Prepare the Mousse: In a microwave-safe bowl, melt 1 cup of semi-sweet chocolate chips until smooth. Let it cool slightly.
11. Whip Cream: In a separate bowl, whip 1 cup of heavy cream and 1/4 cup of powdered sugar until soft peaks form.
12. Combine: Fold the melted chocolate into the whipped cream mixture gently, then add in 1 teaspoon of vanilla extract.
13. Spread Mousse: Once the brownies are completely cool, spread the chocolate mousse evenly over the top.
14. Chill: Refrigerate the brownies for at least 1 hour to allow the mousse to set properly.
15. Garnish: Before serving, top with chocolate shavings or a dusting of cocoa powder, if desired.

Following these steps will lead you to a delicious batch of French Silk Brownies that are sure to impress!