Two.25-ounce envelopesunflavored gelatin(Knox brand, in the Jello aisle)
Instructions
In three separate containers (use rectangular plastic tubs or pyrex loaf pans), mix jello package with 1 cup of boiling water. Stir each until dissolved and then refrigerate until firm (at least 4 hours, or overnight).
Once the jello flavors are firm, use a sharp knife to cut the jello into small squares (½-inch or so).
Spray a 9x13-inch pyrex pan lightly with nonstick spray. Use a metal spatula to scoop out the jello squares and place them into the prepared pan. Mix the colors up so they're not bunched all together.
In a separate bowl, add ½ cup of cold water. Sprinkle in 2 envelopes of gelatin and stir. Add 1½ cups boiling water to the bowl and stir until dissolved. Stir in the sweetened condensed milk and let cool.
Pour the cooled white gelatin mixture over the cubes of jello and let it fill up the pan. Refrigerate overnight. Slice the jello into squares and serve. These are firm enough to serve on a platter as a hand-held dessert.