Has anyone tried using Royal icing on cupcakes and brownies successfully? I tried putting on a batch of brownies but it doesn’t seem like my icing is drying enough for me to use edible pens on it. My pens sink in the icing even after drying for 24 hours. Is it because my brownies are too moist?

well your brownies are delicious I'm sure -- they are maybe not too moist but yes the moisture from the brownies is keeping the royal from setting up -- you could use a layer of crispy dried fondant