Rainbow Jello Cake

• Note: This cake will end up having 11 layers: 5 colored layers (red, orange, yellow, green, blue, purple) and 5 white layers between each color. This recipe isn't hard, but there are lots of steps. Give yourself some grace, read through the entire recipe and tips first, and you'll nail it!
• Prepare the Pan: Spray either a 9x13-inch pan or a 10-cup Bundt pan generously with non-stick spray. This ensures your Jello cake pops out beautifully! Set aside.
• Red Layer: In a large bowl or liquid measuring cup, combine 1 package of strawberry or cherry Jello (85g) and 1 teaspoon Knox gelatin (about 3g) with 1 cup (240ml) boiling water. I like to use the same large bowl to make each flavor or Jello! Just give it a quick rinse between flavors so that the colors stay bright and don't mix. Stir until fully dissolved. Gently pour into the prepared pan. Refrigerate for about 20 minutes or until set (I like to gently poke the layer to test if it's firm!)

  Tip: While each layer sets in the refrigerator, prepare the mixture for the next layer and let it cool on the countertop. This helps prevent the layers from bleeding together.
• White Layer: The mixture we make in this step will be sandwiched between each color of Jello. In a large bowl, mix 5 tsp or 2 envelopes Knox gelatin (14g) with 2 cups of hot water (480g) until dissolved. Then add 14 oz (1 can, or 396g) of sweetened condensed milk and stir until combined. Set aside until the mixture cools to room temperature, then pour slightly over 1/2 cup of the white mixture (120ml) or 1/5 of the total mixture over the set red Jello. It helps to pour the mixture over a spoon to let it fall lightly on top of the previous layer. Refrigerate for 20 minutes until firm.
• Orange Layer: Mix 1 package of orange Jello with 1 teaspoon Knox gelatin and 1 cup boiling water. Cool and pour over the milk layer. Refrigerate for 20 minutes until set.
• Repeat Layers: Continue this process with the remaining Jello flavors (yellow/lemon, green/lime, blue/berry, and purple/grape), alternating each with a white condensed milk layer. Make sure each layer is cooled before pouring over the previous one and that each sets properly in the refrigerator before adding the next.

  Note: The white mixture will likely start to set as it sits between layers - when this happens, heat it up in the microwave in 10-second intervals until it's fluid again and easy to pour.
• Final Chill: After the last layer is added, chill for at least 2 hours, if not overnight, to ensure all layers are firmly set.
• Serve: You can either cut the jello cake directly in the pan or flip it onto a cutting board. I prefer flipping it out of the pan. Do NOT dip the pan in hot water to try to help release the jello. The heat will melt the Jello and create a goopy mess (I learned this the hard way!!). Instead, use your fingers to gently pull the sides of the jello from the edge of the pan, then flip it and it should easily separate from the pan. Cut the layered Jello into squares or slices (depending on which pan you used) with a sharp knife and serve with a dollop of whipped cream, sprinkles, and/or fresh fruit on top, and enjoy!