Preheat oven to 350 degrees F. Line a cookie sheet with parchment paper; set aside. In a small saucepan, combine 1/2 cup of the chocolate pieces and 1 tablespoon of the shortening. Cook and stir over low heat until chocolate is melted. Set aside to cool.
In a large bowl, beat butter and sugar with an electric mixer on medium speed until fluffy. Beat in cooled chocolate mixture. Add egg, milk, and vanilla. Beat until combined. Add the flour, cocoa powder, baking powder, salt, and espresso powder. Beat on low speed until just combined.
Shape dough into 1-inch balls. Roll the balls in chopped walnuts. Place balls 1 inch apart on prepared cookie sheet. Using your thumb, make an indentation in the center of each cookie.
Bake in the preheated oven for 8 to 10 minutes or until edges are firm. Transfer cookies to a wire rack; let cool. Spoon a cherry with some of the sauce into cookie centers. In the same small saucepan, heat and stir remaining chocolate pieces and shortening over low heat until chocolate melts and mixture is smooth. Cool slightly. Drizzle chocolate mixture over tops of cookies. Let stand until chocolate is set. Makes 36 to 40 cookies.