Add ¾ cup (85 grams) vanilla buttercream frosting to a piping bag fitted with a small round tip. Stir the green food coloring into the remaining 2¼ cups (255 grams) frosting until it is the desired shade of grassy green, then transfer to a piping bag fitted with a star tip. Add the chocolate buttercream frosting to a piping bag fitted with a medium round tip.
2. Step
Make the marshmallow ducks: Cut 6 marshmallows in half lengthwise.
3. Step
Cut a marshmallow in half diagonally lengthwise to make 2 triangles. Press the cut sides of the marshmallow back together, then slide the top marshmallow halfway down the bottom marshmallow to make the shape of an hourglass on its side. Press the cut side of a vertically halved marshmallow onto the outer, downward-pointed side of the hourglass shape. This makes the tail, body, and neck of the mallard.
4. Step
Pipe 1 tablespoon of vanilla buttercream onto each cupcake and spread evenly. Place a mallard shape onto the center of a cupcake, pressing down gently into the buttercream. Repeat with the remaining marshmallows and cupcakes. Place the cupcakes on a baking sheet and freeze for at least 1 hour, or until the marshmallows are firmly attached to the cupcakes.
5. Step
Working 1 at a time, quickly dip the top of each cupcake into the melted chocolate until the marshmallows are completely covered, letting the excess chocolate drip off for a moment before turning right-side up and returning to the baking sheet. Freeze for another 30 minutes, or until the chocolate has set.
6. Step
Meanwhile, make the mallard heads: Divide the green fondant into 12 1-teaspoon pieces and roll into smooth balls. Divide the yellow fondant into 12 ¼-teaspoon pieces and use your fingers to form into beak-shaped cones.
7. Step
Lightly wet the base of a yellow fondant beak and press into the middle of a green fondant ball, then use a dab of buttercream or water to press 2 black nonpareils above the beak as the eyes. Repeat with the remaining fondant and nonpareils.
8. Step
Remove the cupcakes from the freezer. Pipe ¼ teaspoon of chocolate frosting in a triangle on each side of the chocolate mallard body and spread into a wing shape. Pipe about ½ teaspoon of white frosting in a circle on top of a mallard neck and place a fondant head on top, pressing gently to adhere. There should be a collar of frosting visible where the head meets the neck. Pipe the green frosting around the bottom of the mallard as grass. Repeat with the remaining cupcakes.
