Begin by preheating oven to 350°F (175°C), and place 12 cupcake liners in cupcake pan.

Add 3/4 cup of buttermilk, 1/3 cup melted chocolate chips, and 1 tsp instant espresso powder into a heat proof bowl. Heat in the microwave at power level 7 for 1 minute or over a double boiler until the chocolate has melted.

Whisk together until the ingredients have combined, making sure all the chocolate is melted. The mixture might look a little separated, but it will come together once you add in your dry ingredients.

Sift the dry ingredients into the wet ingredients (3/4 cup all purpose flour, 3/4 cup granulated sugar, 1/3 cup cocoa powder, 1/2 tsp salt and 1/2 tsp baking soda) into chocolate espresso mixture, and stir until combined.

Scrape the sides and bottom of the bowl as needed with a spatula.

Add 2 large eggs, 1/3 cup vegetable oil, 1 tsp vinegar, and 1 tsp vanilla, and mix just until the batter is smooth.

Fill cupcake liners 3/4 full and bake for about 18-19 minutes, or until a toothpick comes out with a few moist crumbs.

Allow the cupcakes to cool for 5 minutes in the pan before moving them to a cooling rack to finish cooling.

Beat 1/2 cup of unsalted butter on a medium speed for 30 seconds with a paddle attachment, until smooth. 

Mix in 1 tsp vanilla extract and 1/2 tsp salt on a low speed.

Slowly add in 1 1/2 cups powdered sugar in two installments. Add 1/4 cup of heavy cream half through adding in the powdered sugar to make it easier to mix.

Mix in 1/2 cup of cooled, melted dark chocolate.

Beat on low until the ingredients are fully incorporated, and the desired consistency is reached.

If the frosting is too thick, add an extra Tbsp of heavy cream. If it's too thin, add in another 1/2 cup of powdered sugar.

Stir by hand with a rubber spatula to get the frosting SUPER smooth.

To decorate these mushroom cupcakes, pipe a small swirl of chocolate frosting onto each cooled cupcake.

Sprinkle some chopped oreos, poppy seeds, nuts, and pistachios to look like a mossy forest floor.

Shape 18 small mushrooms using marzipan. Roll out the stems press a toothpick through the center. Shape the mushroom tops, then connect them to the stems using the top of the toothpick. If desired, brush the tops with a bit of cocoa powder using a small paint brush. Press them gently into the frosting.