Step 1: Prepare the Cupcakes

1. Preheat your oven to 350°F (175°C). Line a 12-cup muffin tin with cupcake liners.
2. In a medium bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.
3. In a large mixing bowl, beat the butter and sugar until light and fluffy, about 2 minutes. Add the eggs, one at a time, mixing well after each addition. Stir in the vanilla extract.
4. Alternately add the dry ingredients and the buttermilk, starting and ending with the dry ingredients. Mix until just combined—do not overmix!
5. Divide the batter evenly among the cupcake liners, filling each about 2/3 full.
6. Bake for 18-20 minutes, or until a toothpick inserted in the center comes out clean. Let the cupcakes cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.

Step 2: Make the Frosting

1. In a large bowl, beat the butter until smooth and creamy, about 2 minutes.
2. Gradually add the powdered sugar, beating well after each addition.
3. Stir in the vanilla extract, then add heavy cream or milk, 1 tablespoon at a time, until the frosting reaches a fluffy consistency.

Step 3: Assemble the Bunny Bum Decorations

1. If using fondant, roll small pieces into two oval shapes for the feet and one small ball for the tail.
2. Tint a small amount of fondant with pink food coloring and shape tiny circles for the bunny’s paw pads. Attach them to the feet using a dab of water.
3. If using marshmallows, cut one large marshmallow in half for the feet and roll a small piece into a ball for the tail. Attach pink paw pads using a bit of frosting.

Step 4: Decorate the Cupcakes

1. Pipe or spread a generous amount of frosting onto each cupcake. If you want a fluffy effect, sprinkle shredded coconut over the frosting.
2. Place the bunny tail (fondant or marshmallow ball) in the center of each cupcake.
3. Position the bunny feet slightly below the tail, making it look like the bunny is burrowing into the cupcake.
4. Serve and enjoy!