Preheat your oven to 350°F (175°C) and grease a 9-inch round cake pan. In a large mixing bowl, beat together unsalted butter with both granulated and brown sugars until fluffy and light, about 3-4 minutes.

Add in the egg and vanilla extract, mixing well. In another bowl, combine the dry ingredients with buttermilk, then gradually pour the mixture into the wet ingredients.

Pour the batter into the prepared pan and bake for 22-25 minutes, or until a toothpick comes out clean. Allow to cool completely.

For the cinnamon mousse, gently melt cinnamon chips with heavy cream in a saucepan over low heat until smooth. Stir in the canned pumpkin puree until fully combined.

Prepare the unflavored gelatin according to package instructions, then combine with the pumpkin mixture. Fold in the whipped cream gently until well blended.

Spread the cinnamon mousse over the cooled chocolate cake.

For the pumpkin-butterscotch mousse, melt butterscotch chips with part of the heavy cream in a saucepan until smooth. Allow to cool before mixing in the prepared gelatin.

Gently fold in the whipped cream, then layer this mousse over the cinnamon mousse.

Next, melt the salted caramel chips with the remaining heavy cream, mix in thick salted caramel sauce, and allow to cool before incorporating the prepared gelatin.

Fold in the whipped cream to achieve a fluffy consistency. Spread this caramel mousse over the pumpkin-butterscotch layer.

Prepare ganache by heating heavy cream until simmering and pouring it over chopped semi-sweet chocolate, whisk until smooth and cool.

Pour the ganache over the layered mousses, letting it cascade down the sides of the cake.

Cover the cake with plastic wrap and refrigerate for at least 4 hours, preferably overnight.

Once chilled, remove from refrigerator, and top with a dollop of whipped cream, ground cinnamon, and optional chocolate candies.

Use a hot knife to cut through the layers for clean slices.