Make sure the bowl and whip from your stand mixer is completely clean and grease-free. If necessary, wipe down with a paper towel and lemon juice.
Combine meringue powder, powdered sugar and water in the bowl of a stand mixer fitted with the paddle attachment. Beat on low speed until incorporated, add in corn syrup, then beat on medium high for 5 minutes.
Once royal icing is whipped to desired consistency, separate it into three different bowls. About 2/3 of the icing will be tinted pumpkin. Add water, a teaspoon at a time, until desired flood or 20-second icing consistency. Add pumpkin pie spice and combine.
For the pie crust color, mix a small amount of warm brown with ivory to get desired color. Add a small amount of water to the pie crust color, so you have an easy flowing, but still stiffer consistency icing. The smallest amount of icing remains white.
Place pumpkin icing into piping bags. (You can use tipless or a #2 piping tip. Place the pie crust icing into a piping bag fitted with a #104 petal tip. Place the white icing in a piping bag fitted with a #16 or #18 piping tip. Cover the open tips with a wet paper towel while piping the pumpkin.
Outline and flood the entire cookie with pumpkin icing. Let dry completely. Pipe the pie crust, with the small side facing out. Pipe a small rosette of white icing for whipped cream. Let dry completely.