3/4 cup (1 1/2 sticks, 6 ounces) butter
1 cup + 2 tablespoons (7 7/8 ounces) sugar
1/2 teaspoon espresso powder, optional
1/2 teaspoon salt
1/2 teaspoon baking powder
1 large egg
1 tablespoon (1/2 ounce) water
1 teaspoon vanilla
1 1/2 cups (6 1/4 ounces) King Arthur Unbleached All-Purpose Flour
3/4 cup (2 1/4 ounces) Dutch-process cocoa powder

In a large bowl, cream the butter and sugar together till smooth. Beat in the espresso powder, salt, and baking powder, then add the egg, water, and vanilla and beat for at least 2 minutes, until the mixture has lightened both in color and texture. Mix in the flour and cocoa, divide the dough roughly in half, with one piece slightly larger than the other. Shape each half into a flattened disk, being sure to smooth the edges; smooth edges make it less likely dough will crack around the edges as you roll it. Wrap in plastic wrap, and refrigerate for 3 to 4 hours, or overnight. This dough is very soft, so it's imperative that it's cold when you roll it out.
Preheat your oven to 325F. Lightly grease (or line with parchment) two baking sheets.
On a clean, heavily floured work surface-a silicone rolling mat is ideal-roll the larger piece of dough 1/8-inch thick, and use the plain linzer cutter to cut circles. This isn't imperative, and don't make yourself crazy counting, but try to cut about 36 to 40 circles. Place the cookies on the prepared baking sheets. They won't expand a great deal, so you don't need a lot of space between them. Repeat with the other piece of dough, using the cutter with various linzer shapes attached. Again, try to cut about 36 to 40 circles; you'll probably need to gather and re-roll the little center scraps that come out of the linzer cutter as you use it. Place the cookies on the prepared sheets.
Bake the cookies for 17 to 18 minutes. (Watch them carefully; it's really difficult to tell when they're done, as they're so dark you can't see if they're brown, but when you start to smell them they're probably done. And, if you smell even a whiff of scorching, grab them out of the oven quick.) Transfer the cookies to a cooling rack(8492), and cool them completely.
1 cup (4 ounces) confectioners' or glazing sugar
4 teaspoons milk
4 teaspoons light corn syrup
food color (gel paste makes the most vivid colors)
To fill and finish the cookies: Put 1/4 cup confectioners' sugar into each of four tiny bowls. Add 1 teaspoon milk and 1 teaspoon corn syrup to each bowl. Stir until you've made a soft, spreadable icing, adding more milk if necessary. Tint the icing in each bowl a different color (leaving one bowl plain, to make white moons, if desired). Go easy if you're using gel paste colors; a little goes a long way! Spread filling on each of the solid "bottom" cookies. Immediately top with one of the cutout "top" cookies. Allow the filling to harden before storing the cookies. Yield: about 3 dozen filled linzer cookies.