In a microwave-safe bowl heat 1 cup of water for 2 1/2 minutes (until boiling). You can also use a saucepan on the stove over medium heat.
In a large bowl add white flour, salt, cream of tartar, and one 3 oz packet of Jell-O. Stir to combine.
Carefully add the boiling water and oil to the flour mixture. Stir until all ingredients are well combined and a ball of dough begins to form. If the dough is still sticky, add 1-2 Tbsp of flour at a time, and mix well until the dough is no longer sticky.
Place on a piece of parchment paper until the dough is completely cooled (at least 20 – 30 minutes)
Repeat steps 1-4 until all the Jell-O rainbow colors are made.
Notes
Each color of Jell-O makes about 4 C of play dough. The recipe can easily be cut in half.Before giving the dough to your kids, check its texture and consistency. If it starts to feel dry, you can add a few drops of oil and knead it to restore its softness.