Heat oven to 325°F. 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 in center of each cookie.
Bake at 325°F. 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 teaspoon warm caramel mixture into center of each cookie. Cool completely.