DH has made this few times. It is always a hit.
Margarine
Flour
1 package (2-layer size) white cake mix (plus ingredients from boxed
mix)
1 package (4-serving size) JELL-O brand gelatin, any red flavor
1 cup boiling water
1/2-cup

water
3 1/2 cups (8-ounce container) Cool Whip brand whipped topping, thawed
1 pint strawberries, washed and sliced
1-cup blueberries, washed
1-cup miniature marshmallows
Grease 13 x 9 pan with margarine and dust lightly with flour.
Prepare, mix and bake cake mix according to package directions. Cool
cake for 15 minutes. With large fork, make holes in cake about every
1/2 inch. Pour gelatin into mixing bowl. Add cup of boiling water and
use scraper to mix thoroughly until gelatin is completely dissolved.
Use measuring cup to pour gelatin over cake. (It will run down into
holes, making sliced cake have red stripes.) Chill cake in
refrigerator 3 to 4 hours. Cover a large baking sheet or cutting board
(larger than the 9x13 pan) with aluminum foil. Put about one inch of
warm water in kitchen sink. Take pan out of refrigerator and dip
bottom (don't let water come up over sides) into water for about 10
seconds. Put large tray on top of cake, and invert. Frost sides and
top with whipped topping. Arrange strawberries and marshmallows in
alternating rows for stripes, leaving upper left for field of
blueberries. Chill again until time to serve.