My boss wants me to decortae these cookies with mergingue powder. So we got some merigingue powder by wilton. I followed the recipe and the cookies dried all spongy and were still sticky the next day! Next we tried royal icing mix when i used this the frosting turned yellow! Ugh I had to make the cookies for a third time! I used egg white powder and they came out great. My boss says she sees they might be turning a little yellow on the edges... ugh.. and thinks i should put lemon juice in the roayl icing to prevent it from turning color. What do you use to ice your cookies while decorating to get a smooth shiny finish?
shortbread has alot of butter and is generally just decorated with sugar.
i suspect the butter is being absorbed into the icing, turning it off white. it may help to brush the cookies with a glaze first to seal them, and then decorate. the glaze is just powdered sugar, corn syrup and milk, made really thin and brush on.