1Heat oven to 350°. Grease bottom and sides of jelly roll pan, 15 1/2x10 1/2x1 inch, with shortening. Mix granulated sugar, butter, vanilla and eggs in medium bowl with spoon. Stir in flour and baking powder until dough forms. Reserve 1/4 cup dough; cover and refrigerate. Pat remaining dough evenly in pan, using floured hands.
2To make flag design, mark a 6x5-inch outline in upper left corner of pan, using toothpick, for "star" area. Spread blackberry jam over 6x5- inch area. Starting 1/4 inch from top of "flag" (long side of pan), mark stripes by pressing 1/2-inch-wide and 1/4-inch-deep groove into dough with end of wooden spoon or finger. Make 7 more grooves, each about 3/4 inch apart. Place strawberry jam in resealable plastic food-storage bag; cut off tip. Squeeze jam into grooves.
3Pat reserved dough to 1/8-inch thickness on lightly floured surface. Cut with small star-shaped cutter. Place stars on blackberry jam.
4Bake 18 to 22 minutes or until golden brown. Cool completely, about 1 hour. Sprinkle with powdered sugar. For bars, cut into 8 rows by 7 rows.