These cookies come in all shapes and sizes, but are usually composed of a dough encasing a rich fillings such as fruit preserves, buttercream, nuts, chocolate or cooked dried fruit.

Many filled and sandwich cookie recipes are as old as the hills and have a well nested place in tradition - Linzer, Thumbprints Kolaches, Rugelach, Peanut Butter Blossoms, "Oriol" Cookies, and more.

There are some tips I learned from my baking mentor Nick Malgieri when making filled and sandwich cookies: from Cookies Unlimited, by Nick Malgieri, HarperCollins  

1. Make sure the dough is firm but malleable before trying to shape filled cookies. Success depends on having the dough and filling approximately the same consistency so they do not oppose each other as you are trying to shape the cookies;

2. Be accurate about dimension. Use a ruler for best results;

3. Prepare both dough and filling in advance -- then you can concentrate on shaping the cookies on the following day, or whenever you plan to do it;

4. Apply egg wash sparingly on the outsides of cookies. I dip a brush into the beaten egg, then wipe several times against the rim of the bowl or cup containing the egg. This is to make the excess egg drip off so that when you paint the wash onto the cookies it will not dribble down and puddle underneath them;

For sandwich cookies:

1. Try and make all the cookies the same size -- this is easy if you use a cutter. If you are sandwiching drop cookies it's a little more difficult. In that case, scrupulously measure the amount of batter you drop for each cookie. That way they'll have a better chance of being uniform in size;

2. Cool cookies completely before attempting to sandwich them -- especially if the filling is chocolate or buttercream;

3. Use a small amount of filling in each cookie. Usually between 1/4 and 1/2 teaspoon is enough. If you use more, it will squish out when you bite into the cookie;

4. Finish sandwich cookies simply. If the instructions call for sprinkling the cookie with confectioners' sugar, use a little -- or else it will be all over your clothes, not on the cookie;

5.  Keep sandwich cookies in a cool place -- or wait until the day you intend to serve them to sandwich them. Thin fillings can't stand heat or moisture.