Preheat the oven to 350°F and line your cupcake tins with liners.
Using a stand mixer, cream together the sugar and butter until light and fluffy. Beat in the eggs one at a time.
In a small bowl, combine the flour, salt, baking soda, and baking powder.
Gradually add the flour mixture and milk to the butter mixture, alternating in 1/4 cup increments, until the batter reaches a thick yet smooth consistency. Stir in the vanilla extract.
Transfer half of the batter to another bowl and set it aside. Add the cocoa powder to the remaining batter in the mixer and beat until the chocolate is completely incorporated, scraping the sides as you go.
Spoon the cupcake batter into each liner, filling them a little less than 2/3 full. Bake for 20-30 minutes, or until a toothpick inserted into the middle of each cupcake comes out clean.
Once cooked, let the cupcakes cool in the pan on a wire cooling rack until they reach room temperature. Then, place them in a large baggie or airtight container and freeze for 5-8 hours.
After the cupcakes have frozen, use a melon baller to scoop out the center of each cupcake. Place the cupcake holes into a separate baggie or container and return them to the freezer.
Fill each cavity with either the buttercream icing (recipe follows) or Nutella. Cover each filled cavity with green icing.
Remove the cupcake holes from the freezer and gently press one into the green icing on each cupcake. Use a piping bag with a grass or star tip to pipe icing around the cupcake hole, creating a grass-like texture.
Take two matching candy feet (recipe follows) and press them into the icing on either side of the bunny butt. Place a gummy carrot on top.
Cut each mini marshmallow in half and put a pea-sized bit of icing on the sticky end. Press them onto the bunny butt to create tails. Decorate with sprinkles, serve, and enjoy!