Combine the vegan margarine and brown sugar in the bowl of an electric mixer until creamed.
Add the remaining ingredients and beat until well incorporated.
Split the dough in half and wrap in plastic wrap. Flatten into rounds. This will help them chill more quickly and evenly.
Chill for several hours or over night.
Preheat oven to 350 degrees.
On a floured surface, roll the dough to about 1/4" thick and cut out your shapes.
On a parchment or Silpat lined sheet pan, place the shapes and bake for approximately 5-6 minutes. This will depend on how large your cutouts are.
Cool on a wire rack completely.
In a bowl, combine the powdered sugar, corn syrup and almond milk with a fork until smooth. If it is too thick, add more almond milk 1/2 tsp at a time. If it is too thin, add more confectioners sugar 1 tsp at a time.
The icing should maintain its shape when drizzled but eventually 'heal' or settle back into itself. Test a cookie or two and wait a few minutes to see if it's too runny before proceeding.
I use a small round tip to outline and then fill in the cookies.
Tint the icing to make a variety of colors. The gel food coloring does not affect the consistency of the icing at all.
Allow to air dry until hardened. At this point, you can choose to use edible food color markers if desired.