Spray a 9x13-inch baking dish lightly with nonstick cooking spray.

Mix 1 3-oz package of Jello with 1 1/4 teaspoons unflavored gelatin. Add 1 cup of boiling water and stir until dissolved. Pour into the prepared pan. Refrigerate for 20 minutes.(Make sure the shelf is level!)

Meanwhile, mix the can of sweetened condensed milk with 1 cup of boiling water.

In another bowl, combine 1/2 cup cold water and 2 packages of the unflavored gelatin. Let stand for 2-3 minutes. Add in 1/2 cup boiling water and stir to dissolve. Add the sweetened condensed milk and let the mixture come to room temperature. (If the mixture ever sets up too much during the process, stick it in the microwave for 5-7 seconds to loosen it back up.)

After the first layer of Jello has set up for 20 minutes, pour 1 cup of the sweetened condensed milk mixture evenly over the layer of Jello. Return to the refrigerator for 20 minutes.

Repeat the Jello steps above to create another layer of Jello. Refrigerate for 20 minutes.

Continue to repeat until you have 4 layers of Jello and 3 layers of the sweetened condensed milk mixture. Keep refrigerated until completely set up. Cut into squares or desired shapes for serving.

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method mostly taken from Our Best Bites