How to Make It
Using a fork, stir together cold water and gelatin in the bowl of a heavy-duty electric stand mixer fitted with the whisk attachment. Let stand until ready to use.
Combine granulated sugar, tap water, and corn syrup in a large saucepan. Cook over medium-high, stirring occasionally, until small bubbles form on sides of pan. Cook without stirring until a candy thermometer inserted in mixture registers 238°F, 7 to 8 minutes. Add to gelatin mixture in mixer bowl. Beat on medium-low speed until gelatin melts and mixture is foamy, about 1 minute. Beat in vanilla until incorporated. Increase speed to high; beat until stiff peaks form and mixture triples in volume, 8 to 9 minutes.
Fit a large piping bag with a 1/4-inch piping tip. Place sanding sugars separately in 3 shallow dishes.
To make Peeps: Fill piping bag with marshmallow mixture. To make the base of the Peep, pipe a 3-inch oval on yellow sanding sugar in dish. Pull the bag away quickly to form a tail. To make the head and the beak, start at 1 end of oval, and pipe a small “S” shape vertically, pulling bag away quickly to form a beak. Sprinkle yellow sugar over top and sides of Peep. Using a slotted spoon, transfer Peep to a baking sheet. Let stand until set. Repeat procedure, using yellow or pink sanding sugar as desired.
To make the Peeps’ eyes: Follow package directions to melt black candy melts. Dip the tip of a wooden pick into black melted candy; dot each side of Peeps’ heads with melted candy. Let stand until set, about 20 minutes.
To make Bunny Butts: Pipe a 2-inch round of marshmallow mixture on white sanding sugar in dish. Without pulling the tip away, stop piping. Move piping tip to top of round, and pipe a smaller round in the center of the larger round to form a tail. Quickly pull bag away. If a string of marshmallow mixture is left between tail and piping bag, smooth the surface of the tail with a slightly moistened fingertip. To make the feet, hold the piping tip close to the bottom of the larger round and slightly to the left of the tail. Pipe a “foot” about 1/2 inch high; quickly pull bag away. Smooth any strings with a slightly moistened fingertip. Repeat procedure slightly to the right of tail to make the second foot. Sprinkle white sugar over tops and sides of butt and feet. Using a slotted spoon, move Bunny Butt to a baking sheet. Let stand until set.
To finish the Bunny feet: Follow package directions to melt pink candy melts. Transfer melted candy into a piping bag; cut a tiny hole in the tip of the bag. Make a dot about the size of a peppercorn in the center of each foot, and make 3 smaller dots below each larger pink dot to make the toes. Let stand until set, about 20 minutes.