For the Cake:
- Preheat the oven to 350°F (175°C).
- Grease the bottoms of two 8- or 9-inch round cake pans and line them with waxed paper.
- In a large mixing bowl, combine the flour, ground chocolate, granulated sugar, baking soda, cream of tartar, and salt.
- Add 1 cup of buttermilk and 1 cup of softened butter. Beat on medium speed for 2 minutes.
- Add the remaining 1/2 cup of buttermilk, eggs, and 1 teaspoon vanilla extract. Mix until well combined.
- Divide the batter evenly between the two prepared pans.
- Bake for 30 to 45 minutes, or until a toothpick inserted into the center comes out clean.
- Cool the cakes in the pans on a wire rack for 10-15 minutes.
- Remove the cakes from the pans, discard the waxed paper, and let them cool completely on the wire rack.
For the Buttercream Frosting:
- In a large bowl, cream together the butter, shortening, and vanilla extract until smooth.
- Gradually blend in the confectioners’ sugar, one cup at a time, beating well after each addition.
- Add the milk and continue mixing until the frosting is light and fluffy. Cover the frosting until ready to use.
Assembling the Mini Cakes:
- Once the cakes are completely cooled, use a round cookie cutter or a knife to cut out small, even layers from the cakes.
- Spread a layer of buttercream frosting between each cake layer.
- Frost the outside of the mini cakes with the remaining buttercream.
- Decorate with pastel-colored sprinkles, edible flowers, or mini Easter eggs for a festive touch.