Center a rack in the oven to 350°F. Spray a nonstick cupcake pan or mini cake pan with nonstick cooking spray.: The warm oven gradually encourages even rise and caramelization, while the sprayed pan prevents sticking and keeps the bottoms intact. You will smell a faint toasty warmth as the oven reaches temperature, and preparing the pan now saves time later. One common mistake is inserting pans before the oven is fully preheated, which can lead to uneven baking, so wait until the oven registers the correct temperature.
In a large bowl, sift together the flour, baking powder and salt.: Sifting aerates the flour and distributes the baking powder and salt evenly, which promotes a consistent rise and tender crumb. You should notice a light, powdery texture and a faint wheaty scent as you work. Avoid packing the flour into measuring cups, as this can make the cakes dense.
In a medium bowl, whisk together the milk and egg whites.: Combining room temperature milk and whipped egg whites ensures a smooth emulsion that blends into the batter without clumping. The mixture should look glossy and uniform, and it will help hydrate the dry ingredients. A frequent error is using cold liquids, which can cause uneven mixing and a heavier texture.
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.: Creaming butter , sugar , and scraped vanilla bean seeds aerates the fat and creates tiny air pockets that translate into lift. You will see the mixture lighten in color and become fluffy, and the room will smell warmly sweet. Avoid under-creaming, because it can result in a tighter, denser crumb.
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.: Layering wet and dry ingredients helps prevent overmixing, which keeps the cake tender. You will see the batter come together in stages, smooth and slightly glossy, and it should fall slowly from the paddle. Overworking at this stage develops gluten and makes the cake chewy, so mix only until combined.
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.: That final beat helps homogenize the batter and build a consistent structure. As you scoop, the batter should hold a soft mound and glide off the scoop. Filling to two thirds gives room for rise without overflow. A common misstep is overfilling, which causes domed, split tops.
Bake for 18-22 minutes, or until a toothpick inserted into the centers come out clean. Cool on wire rack.: As they bake, the cakes will set at the edges and develop a faint golden top, releasing a comforting vanilla scent. Use a toothpick to confirm doneness, and transfer to a wire rack so air circulates and prevents soggy bottoms. Opening the oven too frequently can cause uneven rise, so resist peeking until the time nears completion.
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.: Whipping the frosting butter invites air into the mixture, producing a light texture. Gradually adding sifted powdered sugar prevents a dusty cloud and ensures a silky consistency. If you add the sugar too quickly, the kitchen will be messy and the frosting may be grainy.
Add in vanilla, and 1 tablespoon of heavy cream or milk. Blend on low speed until moistened.: Introducing clear vanilla extract and a small measure of heavy cream softens the frosting and layers in flavor. The frosting will sheen slightly as it becomes moist, signaling the right balance. Too much liquid at once can make the frosting runny, so add slowly.
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.: High speed whipping builds a cloudlike structure that pipes and spreads easily; you will hear a steady whir and see the frosting double in volume. Adjustments by teaspoon help you dial in spreadability without over thinning. A typical error is adding too much cream too fast, which makes the frosting collapse.
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.: Trimming creates a stable base for stacking and ensures even layers; the cut surfaces should feel springy but set. I always taste a scrap or two to check texture. Cutting while cakes are still warm can cause tearing, so wait until they are cooled to the touch.
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.: When you pipe, use steady pressure to form an even cushion of frosting, then gently press the second layer down to bond. You will hear a soft squish and see the frosting spread to the edges, visually confirming adhesion. Pressing too hard can squeeze out filling and make the cakes unstable.
Top with additional frosting and decorations such as edible Easter grass, pastel sprinkles and Campfire® EggSwirlers.: The final adornment adds color, texture, and whimsy, turning simple cakes into a festive presentation. Place decorations lightly so they rest on the frosting rather than sinking, and enjoy the playful crunch and look. Avoid heavy decorations that tip the cakes or dampen the frosting.