Set the racks in the upper and lower thirds of the oven and preheat to 350 degrees. Pour the melted butter into a bowl; 1 at a time, stir in the remaining ingredients, except the chocolate, stirring smooth after each addition.
Use a 1/2-teaspoon measure to drop the batter on the prepared pans. Space the cookies about 3 inches apart in all directions, to allow room for them to spread. Bake the cookies for about 8 to 10 minutes, or until they have spread and are brown around the edges and lighter toward the center. Slide the paper or foil onto racks to cool the cookies.
When the cookies are completely cool, peel them off the foil and arrange half of them bottom side up on a pan. Use a small offset spatula to spread about 1/2 teaspoon of chocolate on each inverted cookie. Top with another cookie, bottom to bottom. Store the finished cookies between sheets of parchment or waxed paper in a tin or plastic container with a tight-fitting cover.