Prepare and bake the brownies according to the package instructions. Let them cool completely.

While the brownies are cooling, whip the heavy cream with powdered sugar and vanilla extract until stiff peaks form. Set aside.

In a microwave-safe bowl, melt the chocolate chips in 30-second intervals until smooth. Let it cool slightly.

Cut the cooled brownies into small cubes.

In a glass dish or loaf pan, start layering: first, a layer of brownie cubes, then spread a layer of whipped cream, drizzle some melted chocolate, and sprinkle crushed biscuits.

Repeat the layers until all ingredients are used, ending with a whipped cream layer on top.

Drizzle chocolate syrup over the top and garnish with chopped nuts if desired.

Refrigerate the cake for at least 4 hours or overnight for best results.

Slice and serve chilled