Beat sugar, eggs, cocoa, oil, salt and vanilla with electric mixer fitted with whisk attachment on medium speed for 3 min.
Combine flour, OREO Base Cake, baking powder and soda in large bowl. Add to egg mixture. Beat on medium speed with paddle attachment until well blended. Fold in OREO Medium Pieces.
Heat convection oven to 325°F. Shape dough into 2 logs, each 15 inches long. Wrap in plastic and refrigerate 30 min. or until firm. Remove from plastic and place logs on parchment paper-lined sheet pan.
Bake 35 to 40 min. or until very firm. Cool completely on pan on wire rack. Lower oven temperature to 300°F. Trim 1 end of each log. Slice each into 28 (1/2-inch-thick) slices. Arrange slices standing upright on pan. Bake 25 min. to dry. Cool completely on pan. Store tightly wrapped at room temperature for up to 1 week.