Yield: about 12 cupcakes
Preheat oven to 350 degrees Fahrenheit and place racks in the upper and lower thirds. Line 12 standard-size muffin cups with paper liners.
Place the butter and sugar in the bowl of a stand mixer fitted with a paddle attachment and beat on medium until very light—almost white—in color, about 4 to 5 minutes. Scrape down the bowl with a silicone spatula.
Beat the egg whites and vanilla in a small mixing bowl to blend. With the mixer on medium speed, add egg whites to butter mixture about 1 tablespoon at a time, allowing each addition to completely blend in before adding the next. About halfway through, turn off the mixer and scrape down the bowl, then resume adding the egg whites. Scrape down the bowl again.
Using a fine mesh strainer, sift the flour, baking soda and salt into a medium mixing bowl and whisk together. With the mixer running on the lowest speed, add flour mixture and sour cream alternately, beginning with one-third of the flour mixture and half the sour cream. Repeat, then finish with flour mixture. Scrape down the bowl and finish blending the batter by hand, if necessary.
Divide batter among muffin cups, filling each cup no more than 2/3 full. Bake until firm to the touch and a toothpick inserted in the center of a cupcake comes out clean, about 15 to 20 minutes. Transfer cupcakes to a rack to cool completely.
To decorate: Coat the tops of each cupcake with an even layer of lemon buttercream about 1/4-inch thick, using a small offset spatula or a pastry bag fitted with a 1/4-inch round tip. Generously sprinkle the frosted portion of the cupcake with the toasted coconut to create the “nest.” Place 2 to 3 chocolate eggs in the center of the nest, pressing gently to adhere, and serve.
Yield: about 3 cups
In the bowl of a stand mixer, fitted with a paddle attachment, add the butter and beat on high speed until light and fluffy, about 2 minutes. Lower the speed, add the confectioners’ sugar and beat until well combined. Scrape the sides of the bowl and add the lemon juice and zest, stirring constantly until well combined. If the mixture is dry, add the milk and beat at medium speed until light and fluffy.