Pre-heat the oven to 350F. Line a pan with cupcake liners or grease it with butter and flour.

Sift the flour, cocoa powder, baking soda, baking powder, and salt together in a large bowl.

In another bowl, mix the oil, coffee, vinegar, vanilla and sugar.

Pour the dry mixture over the wet ingredients. Whisk briefly, until incorporated.

Distribute the batter evenly in cupcake pan. Bake for 15-20 minutes, until a toothpick comes out clean once inserted in the cakes.

Remove from the oven and let it cool.

Chop the milk chocolate finely. Place it in a heat proof bowl.

Bring the heavy cream to almost a boil over medium heat, or heat it in the microwave at 15 second intervals until really hot. As soon as you see bubbles surfacing, you can turn it off.

Pour the hot cream over the chopped chocolate.

Let it stand for a few seconds.

Whisk the ganache until the chocolate has thoroughly melted and you end up with a luscious and smooth mixture.

Let the ganache sit until it comes to room temperature, from 1 to hours. It has to be completely cooled down before filling the cupcakes or adding to the buttercream.

Reserve 170 grams (3/4 cup, 7 oz.) of the ganache for the frosting part. And the rest will be used to fill the cupcakes.

Place the butter in the bowl of an electric mixer.

Cream on medium high speed for about 1 minute, until creamy and smooth.

Add the ganache and mix until combined.

With the mixer off, add sifted sugar, cocoa powder, and vanilla extract.

Mix until incorporated, on low speed.

Whip on high speed once incorporated, for about 1 minute.

If buttercream is too runny, you can add more powdered sugar.

Mix the sugar, egg whites, cream of tartar and salt in a bowl.

Set the bowl over a pot of barely simmering water over medium heat, don't let the bottom of the bowl touch the water.

Whisk the syrup non-stop while it sits in the double boiler.

Keep whisking over the simmering water until it reaches 140F.

That way the egg whites will be in a safe temperature to be consumed.

Remove from the double boiler and immediately begin to whip with an electric mixer for 3 to 5 minutes on high speed until stiff peaks form.

Add vanilla and mix to combine.

Using a small teaspoon, remove the center of the cupcakes.

Pipe or spoon some of the ganache filling in the cupcakes.

Place the Chocolate Buttercream in a piping bag and pipe a mound of frosting on top of the cupcakes.

Process the graham crackers in a food processor to form crumbs.

After piping the Milk Chocolate Buttercream on top of the cupcakes, sprinkle some graham cracker crumbs on the sides of the frosting.

Place the cupcakes in the refrigerator while you prepare the marshmallow frosting.

It’s important to leave the marshmallow frosting to be made at the end, because the fresher the marshmallow frosting, the better. I don't recommend making the marshmallow frosting ahead. Once piped it will hold up pretty well, but if the frosting sits in a bowl or in a piping bag without being piped, it will begin to deflate and won't form a nice shape.

Place the marshmallow frosting in a piping bag fitted with the tip of choice. I used a large open star. Top cupcakes with a bit of marshmallow frosting.

You may use a torch to toast the marshmallow frosting.

Store the S'mores Cupcakes in the fridge for 4 to 5 days.