Heat oven to 325. In large bowl, combine sugar, butter and shortening; beat until light and fluffy. Add vanilla and egg yolk; blend well.
Lightly spoon flour into measuring cup; level off. Add flour, cocoa and baking powder to butter mixture, mix well.
In small bowl, beat egg white until foamy; place pecans in another small bowl. Shape dough into 1 inch balls. Dip in egg white; roll in pecans. Place 2 inches apart on ungreased cookie sheets. With thumb, make indentation of each cookie.
Bake at 325 for 12 to 14 minutes or until cookies are set.
Meanwhile, in small saucepan, combine caramels and half and half; cook over medium low heat until caramels are melted, stirring occasionally.
Immediately remove cookies from cookie sheets; place on wire racks. Spoon 1/2 tespoon warm caramel mixture into center of each cookie. Cool completely.
Makes 4 dozen cookies.