Use this recipe to make the fence for Martha's Spring Garden Cake. Use pastillage just after kneading.
Sift confectioners' sugar and cornstarch into bowl of an electric mixer. Set aside.
In a small bowl, sprinkle gelatin over 2 tablespoons cold water. Let stand 5 minutes.
In a medium heatproof bowl, combine egg white and 1 tablespoon water. Set bowl over a pot of gently simmering water; stir continuously until warm to the touch, about 2 minutes. Remove from heat; add gelatin mixture. Stir until dissolved. If gelatin does not dissolve completely, return mixture to double boiler; stir until completely dissolved.
Remove from heat, and immediately add to cornstarch mixture. Add lemon juice; mix on low until mixture comes together. Do not overmix. If it appears too dry, add a few drops of lukewarm water, if it appears too wet, sprinkle in confectioners' sugar that has been sifted.
Transfer pastillage to a clean work surface dusted lightly with cornstarch. Knead until smooth, 2 to 3 times. Using a pastry brush, dust off excess cornstarch. Form into a ball, and wrap in plastic wrap. Chill up to 24 hours (bring to room temperature before rolling).
To roll, take a small piece of pastillage from the ball; place on a clean work surface dusted with cornstarch (keep the rest wrapped). Roll small piece out to 4 1/2-by-5 1/2-inches and 3/16 inch thick. Cut lengthwise into eight 1/2-inch strips.
For top of fence, cut a half-moon along top edge of pickets; use the edge of a 10-inch bowl as a guide. The longest pickets (on both ends) should be 5 1/2 inches tall, the shortest (in middle) 3 3/4 inches. With a spatula, transfer pickets to a parchment-lined baking sheet to dry at least 6 hours.
Repeat steps 6 and 7 four times.
For posts, roll out a 3/16-inch-thick piece of pastillage. With a paring knife cut into a 3-by-6-inch rectangle. Cut rectangle lengthwise into five 1/2-inch-wide strips. Cut top of each post to a point.
Transfer posts to a parchment-lined baking sheet to dry, at least 6 hours. Immediately after icing cake, apply pickets and posts 1/2 inch apart around perimeter.