1. Make the Chocolate Cakes
Preheat the oven to 350°F (175°C). Line two baking sheets with parchment paper.
In a medium bowl, whisk together flour, cocoa powder, baking soda, and salt.
In a large bowl, cream the butter and brown sugar until light and fluffy. Add the egg and vanilla and mix until combined.
Gradually add the dry ingredients to the wet, alternating with buttermilk. Mix until smooth and thick.
Using a spoon or piping bag, form oval-shaped dollops (~3 inches long) on the baking sheets, spaced about 2 inches apart.
Bake for 8–10 minutes or until they spring back when gently pressed. Let cool on the pan for 2 minutes, then transfer to a wire rack to cool completely.

2. Make the Filling
In a mixing bowl, beat the butter and powdered sugar until smooth. Add marshmallow creme and vanilla, beating until fluffy. Add cream a little at a time until a spreadable consistency is achieved.

3. Assemble the Devil Dogs
Once the cakes are cool, match them into pairs by size. Spread or pipe filling onto the flat side of one cake and top with its pair. Press gently to sandwich them.

4. Serve & Store
Enjoy immediately or chill for 15 minutes for a firmer texture. Store in an airtight container in the fridge for up to 5 days or freeze individually wrapped for longer storage.