Preheat the oven to 375F and line two baking sheets with parchment paper.
In a medium bowl, stir together both flours, baking powder, cinnamon, and salt.
In another bowl, beat the butter, shortening, and brown sugar for about 3 minutes until light and creamy. Add the eggs, buttermilk, and Ã‚Â½ teaspoon vanilla and beat until combined.
In a third bowl, combine the milk, baking soda, and vinegar. Add this slowly to the butter mixture, then add the flour mixture and beat on low speed until completely combined.
Drop about 2 tablespoons of batter onto the baking sheet with a spoon. Each drop should be spaced at least 3 inches apart.
Bake for 10 minutes until the cakes begin to brown. Remove from the oven and let them cool on the baking sheet for 5 min before transferring them to a rack to cool completely. They might break if you try to move them when they are too warm.
Beat together the marshmallow fluff and shortening for 3 minutes until smooth and fluffy.
Reduce the mixer speed and add the powdered sugar and 1 teaspoon vanilla. Increase speed and beat until fluffy.
Place the chocolate in a large, heat proof bowl.
Heat the cream in a saucepan over medium heat just until it bubbles. Pour the heated cream over the chocolate in the bowl and let it sit for about 10 minutes, until the chocolate is just melted. Stir with a whisk until smooth.
Refrigerate for about 30 minutes, stirring every 10 minutes until it is firm enough to spread.
Pair up your cakes by size. Spread the marshmallow cream onto the flat side of one cake and the chocolate ganache on the flat side of another, squish together, and repeat until all cakes are covered.