My mom used to make this for us as kids, so fun. I believe it is the same recipe as "Knox Blox".

Ingredients

3 pkg. Knox gelatin
4 sm. (3 oz.) boxes Jello (any flavor)
4 c. boiling water

Directions

Put Jello and Knox gelatin into a bowl. Add water and stir until dissolved. Pour into 9x13 inch pan. Cool in refrigerator. When firm (about 3 hours), cut into squares.

Note: some recipes call for 4 pkgs knox and 3 packages flavored.

For double decker finger jello (jello on bottom, creamy mix on the top)

Use only 3 cups boiling water to dissolve the gelatin.
Pour gelatin into pan as normal.
Pour in 1 cup (1/2 pint) heavy or light cream.

Note: Pour it in gradually, over the entire surface of the gelatin. Do not try and pour "gently" to facilitate the layering, as this will lead to the cream mix not hardening. Pour from a few inches above the pan so the cream interacts with the gelatin. The layering will take care of itself.