In a large bowl, beat butter with electric mixer on medium to high speed for 30 seconds. Add sugar, baking powder, ground ancho chile pepper, the 12 teaspoon finely ground black pepper, ginger, cloves, cinnamon, and cayenne pepper. Beat until combined, scraping side of bowl occasionally. Beat in egg and milk until combined. Beat in as much of the flour as you can. Using a wooden spoon, stir in any remaining flour. If necessary, knead dough slightly to blend. Shape dough into a ball. Divide dough in half. Shape each half into a 6-12-inch-long roll. Wrap in plastic wrap or waxed paper; chill 4 to 24 hours.
Preheat oven to 375 degrees F. Cut rolls into 1/4-inch-thick slices. Place slices 1 inch apart on ungreased cookie sheet. Sprinkle cookies with medium-grind black pepper. Bake 8 to 10 minutes or until edges are golden. Transfer to a wire rack; let cool.
In a small saucepan, combine chocolate and shortening. Cook and stir over low heat until melted. Dip each cookie halfway in melted chocolate; shake off excess. Place chocolate-dipped cookies on waxed paper. Let stand until chocolate is set. Makes about 60 cookies.