Preheat oven to 350°F (180°C). Spray a 9-inch round cake pan with baking spray with flour. Line bottom of pan with parchment paper.

In a large bowl, whisk together melted butter, sugars, and lemon zest until combined. Add egg and molasses; whisk until well combined.

In a medium bowl, whisk together flour, ginger, cornstarch, salt, cinnamon, cardamom, cloves, baking powder, and baking soda. Gradually fold flour mixture into butter mixture just until combined.

Spoon dough into a large pastry bag; cut a 1-inch opening in tip. Pipe dough evenly into prepared pan. Using a sheet of plastic wrap pressed directly onto surface, spread and press dough into an even layer. Discard plastic wrap.

Bake until edges are golden brown and top appears dry, 13 to 16 minutes. Let cool in pan for 15 minutes. Carefully remove from pan, and let cool completely, parchment side down, on a wire rack. (Center may sink slightly as it cools.)

Spoon green Citrus Buttercream into a pastry bag fitted with a 5/8 -inch open star piping tip (Ateco #828). Spoon red Citrus Buttercream into a pastry bag fitted with a 3/16 -inch open star piping tip (Ateco #821). Pipe green buttercream as desired around edges of cooled cookie. Decorate with red buttercream as desired. Garnish with sprinkles, if desired. Store in an airtight container for up to 3 days, or refrigerate in an airtight container for up to 5 days. If refrigerating, let come to room temperature before serving.