Best Christmas Cookie Icing?

I don't really have any help for this, but I would like the recipe as well.

I always enjoy making holiday cookies.

I generally decorate some cookies with fine white lines (the cookies are ginger snaps, so they're darkish, and the white is a nice contrast).  This is a picture with some of them (bottom right of both dishes - not the cake which is fondant).  I don't use a recipe but put an egg white and add enough sifted powdered sugar to be able to spread or push through a fine hole of a decorating syringe.  I used the same to spread on the tops of the heart sandwiches with the cutout with red jam and I added lemon peel and lemon juice to frosting on the star shaped ones front left.  If this is the sort of decoration you mean, that's a good solution - it flows easily from the tube and can be easily spread, then dries hard.  (You need to leave it uncovered a while). 

Siduri is talking about something which is very common and is called "royal icing."  Google the term, and you'll come up with tons of copies of the recipe (with minor variations), and any number of "how to" videos. 

Royal icing is made in either of two "consistencies," piping and flooding.  Piping is for decorating, and tighter; flooding is for covering the pastry's entire top, and looser. 

Common or not, royal icing is probably the best way to do what you want and it's what most professional bakeries use for decorating holiday cookies. 

Siduri's cookies look great, don't they? 

Hope this helps,

BDL

BDL, you're right!  I forgot that and looked into my xmas notebook and found the original recipe I got in a magazine - except i had to adapt it because it called for meringue powder and i used egg white.  But i forgot it was beaten which is an important thing since that was the trick that made it possible for me to squeeze it out of the tiny decorating tip for the fine lines.  I used to use just powdered sugar and water and it was extremely difficult.  (I use a syringe, never could stand dealing with washing out a cloth bag, they would end up moldy next time and the frosting would come out the back! but using a syringe was painful since i use the same decorated spice cookies for tree decorations, so i make a lot.  With this recipe it's soft yet keeps its shape)., 

I've had royal icing on some cakes (piped thick with a star tip, for instance) and it's totally inedible - hard and unpleasant.  But this, being spread thinly or piped thinly is a very pleasant contrast to the cookie.