Swirl the luscious chocolate-and-pecan mixture through these festive cookies.
In a small saucepan, melt chocolate pieces over low heat; remove saucepan from heat. Stir in pecans; set aside.
In a large mixing bowl, beat butter with an electric mixer on medium to high speed for 30 seconds. Add 2/3 cup sugar and vanilla. Beat until combined, scraping the sides of the bowl occasionally. Beat in the flour and salt until combined.
Spoon chocolate mixture over dough. Stir just until "reveled" or marbled. Drop the cookie dough 2 inches apart onto ungreased cookie sheets using a cookie scoop or rounded teaspoons.
Grease the bottom of a glass. Dip in additional sugar, then press cookies with glass to 1/4-inch thickness. Repeat dipping and pressing for each cookie.
Bake in a 350ºF oven for 10 to 12 minutes or until edges are firm. Cool on cookie sheet for 2 minutes. Transfer to wire racks and let cool.