Center a rack in the oven to 350°F. Spray a nonstick cupcake pan or mini cake pan with nonstick cooking spray.
In a large bowl, sift together the flour, baking powder and salt.
In a medium bowl, whisk together the milk and egg whites.
In the bowl of a stand mixer fitted with the paddle attachment, or with a hand mixer, beat the butter, sugar and vanilla bean seeds at medium speed for 3 minutes, or until the butter and sugar are very light.
Add in the vanilla extract and one third of the flour mixture, still beating on medium speed. Beat in half of the milk-egg mixture, then beat in half of the remaining dry ingredients until well incorporated. Add the rest of the milk and eggs, beating until the batter fully incorporated and smooth, then add the last of the dry ingredients.
Once ingredients are thoroughly incorporated, give the batter a good 2-minute beating to ensure that it is thoroughly mixed and well aerated. Using a large scoop (about 3 tablespoons), distribute the batter between 24 cupcake wells, filling each well 2/3 full.
Bake for 18-22 minutes, or until a toothpick inserted into the centers come out clean. Cool on wire rack.
For the Buttercream
In the bowl of a stand mixer fitted with the paddle attachment, cream the butter on medium speed until light and fluffy; about 5 minutes. With the mixer on low speed, slowly add in the powdered sugar, and continue beating until well blended.
Add in vanilla, and 1 tablespoon of heavy cream or milk. Blend on low speed until moistened.
Beat at high speed until frosting is smooth and fluffy; about 5 minutes. If desired, add in additional milk or heavy cream, one teaspoon at a time, until you reach the desired consistency.
To Assemble the Mini Cakes
Use a knife to cut the domed portion off of each cupcake to create a flat surface. These scraps can be used to snack on or make cake balls.
Pipe prepared frosting onto the cut surfaces of 12 of the mini cakes. Place another mini cake directly onto the frosting to create 12 mini layered cakes.
Top with additional frosting and decorations such as edible Easter grass, pastel sprinkles and Campfire® EggSwirlers.
Notes
I used melted candy melts and sprinkles to add a little dimension to my Campfire® EggSwirlers, but of course, they're still super cute if you omit that step.