Cut margarine very fine into sifted dry ingredients. Add eggs and milk and mix well. (Dough will be soft.) Form into a ball on waxed paper. Wrap and chill overnight. Remove 1/3 of dough and return to refrigerator. Roll rest of dough on well floured board to fit 12 x 15-inch greased cookie sheet. Keep dusting dough with flour so rolling pin won't stick. Roll over cookie sheet. Pat dough up sides also. Spread jam (red colored) over dough. Roll out rest of dough. Place, lattice fashion, on top. Bake at 350 degrees for 35 minutes. Dust with powdered sugar when cool and cut into squares.