In a medium saucepan, combine the chocolate pieces and 2 tablespoons of the butter. Heat and stir over low heat until melted. Let stand at room temperature for 20 to 30 minutes or until cooled. Preheat oven to 350 degrees F.

Meanwhile, in a medium bowl, stir together flour, cocoa powder, baking powder, and salt. Set aside.

In a large bowl, soften the remaining butter; beat with an electric mixer on medium to high speed for 30 seconds. Beat in brown sugar. Add eggs, one at a time, beating and scraping bowl after each addition. Beat in the melted chocolate mixture and the vanilla. Add the flour mixture, beating on low speed until mixture is combined.

Drop dough by well-rounded teaspoons 2 inches apart onto ungreased cookie sheets (dough becomes firmer as it stands). Bake in the preheated oven for 8 minutes. Remove from oven. Lightly press three or four pecan halves onto each cookie, arranging pecans evenly apart and with ends pointing toward center of the cookie. Place a marshmallow half, cut side down, in the center of each cookie with pecan ends under marshmallow.

Return cookies to the 350 degrees F oven for 2 minutes. Remove from oven. Lightly press a pecan half on top of each marshmallow. Let cookies stand on cookie sheet for 2 minutes. Transfer cookies to a wire rack; let cool.

If desired, drizzle cookies with caramel ice cream topping just before serving. Makes 48 cookies.

Use kitchen scissors to halve the marshmallows. If the scissors get sticky when cutting marshmallows, lightly coat them with nonstick cooking spray or dip them in hot water.

Layer undrizzled cookies between pieces of waxed paper in an airtight container; cover. Store at room temperature for up to 3 days or freeze for up to 3 months. Thaw cookies, if frozen. If desired, drizzle cookies with caramel ice cream topping just before serving.