buttermilk powder in the back of your fridge, in which case you can mix the powder in with the dry ingredients and then use water in place.
If you don't happen to have real buttermilk OR buttermilk powder, you can make your own by adding 1 1/2 tsp of lemon juice or White vinegar to 1/2 cup of plain milk. Let it set for about 5 minutes prior to using.
1 1/4 cups all-purpose flour
1 1/4 cups sugar
1/2 cup unsweetened cocoa powder
4 oz. bittersweet chocolate, chopped
1 stick butter, room temp (1/2 cup or 8 Tbs)
1/2 cup buttermilk
2 large eggs, lightly beaten
1 tsp baking soda
1 tsp baking powder
1 tsp vanilla extract
1/2 tsp salt
1 cup mini marshmallows
1/2 cup graham cracker crumbs
Preheat oven to 350º F Line a cookie sheet with silicone cupcake liners (or use paper liners in a muffin tin).
Over a double boiler melt butter and bittersweet chocolate pieces together, whisking gently until smooth, then remove from heat and allow the mixture to cool. Be sure not to get any water into the chocolate and be sure that you don't heat it to high, which will make the chocolate grainy in texture. (Also, While this can be done in the microwave on medium power, chocolate burns very easily which will cause a separation, so if you want to cut out time, do so with caution! Dark Chocolate should never be heated over 120F during the melting process or it will become thick and mud-like, in bakers terms- it will seize!)
In a large bowl combine flour, sugar, cocoa powder, baking soda and salt, mixing well to ensure the ingredients are fully incorporated.
Add the lightly beaten eggs into the lukewarm melted chocolate, whisking well to incorporate, then add vanilla extract and whisk again to ensure it's evenly distributed in the chocolate mixture.
Add half of the flour and half of the buttermilk to the melted chocolate, mixing, then add the remaining flour mixture and buttermilk, whisking gently to incorporate, but do not over mix as this will make the cupcakes tough.
Pour the batter into the silicone (or paper liners), filling them about 2/3rd full each, then top each cupcake with 2 teaspoons of crumbs and 3-4 mini marshmallows, pressing them gently into the batter.
Bake for 19-22 minutes, (if you're unsure as to whether they are done, insert a toothpick into the cupcake, if it comes out clean, it's done!).