1) Preheat the oven to 350°F. Lightly grease (or line with parchment) two baking sheets.
2) Combine the vanilla, baker's ammonia, and salt in a very small bowl. Stir to dissolve the ammonia; the salt won't fully dissolve.
3) Combine the vanilla mixture with the butter and sugar, and beat till smooth.
4) Mix in the flour; the mixture may seem quite dry at first. Continue beating until the dough comes together.
5) Scoop the dough into 1"-diameter, 3/8-ounce balls. A level teaspoon cookie scoop works perfectly here.
6) Space the balls on the prepared baking sheets, leaving about 1 1/2" between them.
7) Use the bottom of a glass, dipped in sugar if necessary to prevent sticking, to flatten the balls to about 1/4" thick. If you have it, use the end of the food pusher from a food processor; many of these have a circular, ridged pattern on their end, which imprints the cookies with a nice design.
8) Bake the cookies until they're set, and a very light golden brown around the edges, about 15 minutes.
9) Remove them from the oven, and leave them right on the pan to cool, as you make the filling.
10) Place the chocolate chips, corn syrup, vanilla, espresso powder, and cream into a large microwave-safe bowl, or into a large saucepan.
11) Heat the mixture till it's very hot; the cream will start to form bubbles.
12) Remove from the heat, and stir until smooth.
13) Beat in the confectioners' sugar.
14) Dollop icing on the flat side of half the cookies, spreading it to within about 1/2" of the edge. You'll use about 4 teaspoons for each cookie; a tablespoon scoop, filled to just below the rim, works very well here.
15) Top each of the iced cookies with a plain cookie, and squeeze gently to push the filling out to the edges.
16) Place the cookies on a rack, or back on the cookie sheet, so the icing can set. Wrap in plastic, and store at room temperature.
Yield: 33 cookies, about 2 1/4" to 2 1/2".