Grease cupcake pans and set aside.: The surface should feel lightly slick to the touch, which prevents the nests from sticking as they cool. I use a small amount of butter rubbed with a paper towel into each cup, and you will notice a faint sheen when it's ready. If you skip this step, the edges can adhere and tear when you remove the nests.
Melt marshmallows and butter in a microwave-safe bowl (I cooked mine for about 2 minutes but kept a close eye and made sure they weren't puffing up too much and falling out of the bowl.): As the marshmallows melt, the aroma becomes sweet and warm, and you will see pockets of glossy liquid forming. Stir frequently to encourage even melting; I stopped mine at about 2 minutes to avoid the marshmallows puffing and overflowing. If you overheat, the mixture can seize and become grainy, so heat in short bursts and stir between each interval.
Stir together until well blended and pour in Rice Krispies. Stir until well combined.: You should hear a soft crackle as the cereal meets the warm marshmallow, and the mixture will look glossy and evenly coated. Use a sturdy spatula to fold, scraping the sides so there are no dry pockets. A common mistake is over stirring, which can crush the cereal and make the texture dense rather than airy, so fold gently yet thoroughly.
Spoon into greased cupcake pan and press down with wax paper.: When you press the mixture into the cups, you will feel a warm, slightly sticky mass that compacts into the nest shape. The wax paper prevents sticking and helps you get even depth without burning your fingers. Press with light, even pressure to create a hollow center for the frosting; pressing too hard makes the treats too firm.
Let set for a half hour.: During this rest the nests cool and firm up, the marshmallow loses surface tackiness, and the structure stabilizes. You will notice the sheen dull slightly and the nests hold their shape when touched. Try not to move the pan while setting, because jostling can create cracks or uneven walls.
Combine butter, milk, vanilla and 2 cups of your powdered sugar in a large bowl. Mix till smooth and creamy, about 5 minutes. Then add the remaining powdered sugar and food coloring of your choice.: As you cream these together, the mixture becomes glossy and slightly airy, and the scent of vanilla extract becomes pronounced. Beat for about 5 minutes until smooth, then incrementally add remaining powdered sugar and the green food coloring to reach the desired thickness and color. If the frosting is too loose, add more powdered sugar a quarter cup at a time; too much powder makes it dry and crumbly.
Pipe your frosting into your cookie cups and top with Easter egg candies. ENJOY!: The texture should be velvety and hold soft peaks when lifted with a spoon, which is a good indicator for piping. You'll see the butter transform from opaque to silky, and tiny air pockets will give the frosting a light mouthfeel. Avoid overbeating which can incorporate too much air and make the frosting collapse when piped.
Then add the remaining powdered sugar and food coloring of your choice: Adding the rest of the powdered sugar tightens the frosting consistency, making it hold shape. Gradually add the green food coloring to control shade and ensure even distribution so you don't get streaks. If the color is uneven, fold lightly until uniform, but try not to overwork the frosting which can cause graininess.
Pipe your frosting into your cookie cups and top with Easter egg candies: The frosting should glide from your piping bag in soft ridges that mimic grass, creating a nest cradle for the Easter Egg Candies . Press the candies in gently while the frosting is slightly tacky so they adhere, and arrange them for visual balance. A common issue is frosting that is too warm and slips; chill briefly to firm it up if needed.
ENJOY!: The finished nests offer a mix of textures, from the crisp Rice Krispies to creamy frosting and crunchy candies, and you'll likely hear delighted exclamations when guests bite into them. Serve at room temperature for the best texture. If you store them improperly, the candies can sink into the frosting or the nests can become soggy, so keep them in an airtight container at cool room temperature.