1. Make the Chocolate Cake Layers:

Prepare three 8-inch round cake pans (grease, parchment bottom, grease/flour). Preheat oven to 350°F (175°C) – Self-correction: Recipe says 300°F. Following recipe. Preheat oven to 300°F (148°C).

Whisk dry ingredients (flour, sugars, cocoa, soda, powder, salt) in a large mixer bowl.

Whisk wet ingredients (eggs, milk/buttermilk, oil, vanilla) in a separate bowl.

Add wet to dry, mix until combined. Slowly mix in hot water/coffee until smooth (thin batter).

Divide evenly between pans. Bake 30-35 mins until toothpick has moist crumbs. Cool 10 mins in pans, then fully on wire racks.

2. Make Graham Cracker Crunchies:

While cakes cool (or after), preheat oven to 350°F (175°C). Line a cookie sheet with parchment.

Combine graham cracker crumbs, sugar, and melted butter. Spread evenly on prepared sheet.

Bake 8-10 minutes until lightly toasted. Cool completely, then break into small, crumbly pieces. Set aside.

3. Make Toasted Marshmallow Frosting:

Spread 1 ½ cups mini marshmallows on a foil-lined baking sheet. Broil on HIGH for about 1 minute, watching constantly, until lightly toasted and puffed. Remove immediately and let cool completely.

In a large mixer bowl (paddle attachment), beat room temperature butter until smooth.

Add marshmallow fluff and beat until well combined.

Gradually add sifted powdered sugar, mixing on low then medium until smooth and combined.

Gently fold or mix in the cooled, toasted marshmallows (break apart sticky clumps first). Set aside.

4. Make Chocolate Ganache:

Place chocolate chips in a medium heatproof bowl.

Heat heavy cream in saucepan or microwave until just boiling/simmering. Pour hot cream over chips.

Let sit 3-5 minutes. Whisk gently until completely smooth and glossy. Let cool until thickened but still pourable/spreadable (room temp or slightly warmer).

5. Make Vanilla Buttercream Dam:

Beat softened butter until smooth. Gradually add sifted powdered sugar. Beat in vanilla and milk/cream until light and fluffy. Transfer to a piping bag with a medium round tip (or just a snipped corner).

6. Assemble the Cake:

Level the cooled cake layers if needed. Place the first layer on a cake plate/board.

Pipe a dam (ring) of vanilla buttercream around the top outer edge of the cake layer.

Spread about 6 tablespoons of chocolate ganache evenly inside the buttercream dam.

Top the ganache with about 1 cup of the toasted marshmallow frosting, spreading it evenly within the dam.

Sprinkle ½ cup of the prepared graham cracker crunchies over the marshmallow frosting.

Place the second cake layer on top. Repeat the process: pipe vanilla dam, spread 6 tbsp ganache, spread 1 cup marshmallow frosting, sprinkle ½ cup crunchies.

Place the final cake layer on top (upside down for flat surface).

Apply a thin crumb coat of the toasted marshmallow frosting over the entire cake. Chill for about 30 minutes until firm.

7. Final Frosting & Decoration:

Frost the top and sides of the chilled cake smoothly with the remaining toasted marshmallow frosting.

Gently press the remaining graham cracker crunchies onto the bottom 1-2 inches of the cake sides.

Re-warm the remaining chocolate ganache slightly if needed to make it fluid for dripping. Apply the ganache drip around the top edge of the cold cake. Flood the top center with ganache and smooth. Let set briefly.

Place extra mini marshmallows on top of the ganache. Use a kitchen torch to lightly toast the marshmallows.

Drizzle lightly with any remaining ganache or caramel sauce (optional). Add extra walnut pieces if desired (Self-correction: Walnuts not listed, ignore).

8. Chill and Serve:

Refrigerate the cake until ready to serve (at least 30 mins for ganache to fully set).

Serve cool, but let sit out briefly from fridge for best texture. Store leftovers covered in the refrigerator.