In 4 separate bowls dissolve one 3oz box of jello in ONE cup of boiling water. Pour into containers and chill. I made mine about 8am and by 7pm they were firm. (my containers are 9x6 Rubbermaid)
After making sure your jello is firm, place 1/2 cup cold water in a medium bowl. Sprinkle your 3 packs of gelatin over the water.
After the gelatin "blooms" add 1&1/2 cups of boiling water and stir with spoon to dissolve. Then add condensed milk stir and let cool on the counter. I've made this bundt twice. The first time I didn't let it cool enough, so my "glass" melted a bit. Second time I waited a little longer and the mixture was a little lumpy, but after it chilled overnight it looked perfect. Point: Let it cool at least past the lukewarm stage.
When milk mixture is just about cool enough, carefully lift your jello out of containers and cut into small cubes. Lightly grease your pan with a little canola oil. Being careful again, place your "glass" in pan. Remember, it's Stained Glass. Mix up your colors!
Gently pour cooled milk mixture over jello. No worries if there are bubbles on top. Cuz that's really the bottom and no ones going to see them!
Put in fridge and chill over night.
Invert onto a serving plate.
Note: Even with a light coat of canola oil in the pan I still had to run a thin knife around the edge to kinda loosen it up. My first batch was made in a 9x13 pan. No oil necessary and only use 2 packs of gelatin. With this one you'll want to try and pop most of the bubbles on top. Cuz it's really the top and people are going to see them! They're beautiful. Thanks Food Librarian!