01 - Preheat oven to 350°F. Generously grease a 9x13-inch baking pan with cooking spray or butter.
02 - Combine vanilla cake mix, water, vegetable oil, and eggs in a large bowl. Beat according to package directions until smooth. Pour batter evenly into prepared pan.
03 - Bake for 28 to 32 minutes or until a wooden toothpick inserted in center comes out clean. Remove from oven and let cool in pan for 15 minutes.
04 - Using the handle of a wooden spoon or a skewer, poke holes evenly across entire surface of cake, spacing about 1 inch apart.
05 - In two separate bowls, dissolve strawberry gelatin in 1 cup boiling water and lemon gelatin in remaining 1 cup boiling water. Stir each until completely dissolved, then add 1 cup cold water to each bowl.
06 - Carefully pour strawberry gelatin over one half of cake and lemon gelatin over other half. Gently spoon into holes as needed to ensure even absorption.
07 - Cover pan with plastic wrap or foil. Refrigerate for at least 2 hours or until gelatin is completely set.
08 - In a chilled bowl, beat heavy cream with powdered sugar and vanilla extract using electric mixer until stiff peaks form.
09 - Spread whipped cream evenly over chilled cake. Decorate with pastel sprinkles or jelly beans if desired. Serve cold.