Preheat your oven to 350°F (175°C). In a large mixing bowl, cream together room temperature unsalted butter, granulated sugar, and brown sugar until fluffy and light, about 3-4 minutes. Beat in the egg and vanilla extract until well combined.

Gradually alternate adding the sifted dry ingredients—flour, cocoa powder, baking soda, and salt—with buttermilk until the mixture is smooth. Pour into a greased 9-inch round cake pan and bake for 22-25 minutes, or until a toothpick comes out clean.

Let it cool completely in the pan on a wire rack.

While the cake cools, prepare the mousse layers. Start by lining a clean 9-inch round pan with acetate to shape the layers.

For the cinnamon mousse, in a saucepan, melt cinnamon chips over low heat with heavy cream, stirring until smooth. Remove from heat and let cool.

Meanwhile, whisk unflavored powdered gelatin with a little water, then heat until dissolved. Stir this into the cooled chocolate mixture before folding in whipped cream softly.

Pour onto the cooled chocolate cake layer and refrigerate for 25-30 minutes to set.

Next, make the pumpkin-butterscotch mousse by mixing canned pumpkin puree with heavy cream and any desired flavoring. Cool the mixture, then combine it with gelatin, ensuring it’s fully dissolved, and gently fold in more whipped cream.

Once combined, add this layer over the set cinnamon mousse, smoothing out the surface. Refrigerate for another 25-30 minutes until firm.

For the salted caramel mousse layer, melt salted caramel sauce with cream. Let it cool slightly before mixing in gelatin and folding in whipped cream for lightness.

Pour over the pumpkin-butterscotch layer and refrigerate for an additional 25-30 minutes, allowing it to firm up completely.

Prepare the chocolate ganache by heating heavy cream in a small saucepan until just simmering. Remove from heat, add chopped semi-sweet chocolate, and let it sit for a minute before stirring until completely smooth.

Allow the ganache to cool slightly to thicken before pouring it over the chilled cake. Spread evenly with a spatula.

Return the cake to the refrigerator and chill for at least 4 hours, preferably overnight.

When ready to serve, gently remove the cake from the pan and peel away the acetate. Decorate the top with dollops of whipped cream, ground cinnamon, and a few chocolate truffles.

Serve chilled and enjoy your beautiful fall dessert!