2 c. cornstarch
1 c. salt
1 tbsp. shortening
1 1/2 c. water
1/2 tbsp of vegetable oil

Mix all of the ingredients in a large stockpot and cook over low heat until mixture leaves edge of pan. It will thicken and be a little hard to stir initially. You can add a little water to it. Take it out and knead it while still warm, adding food color, if you like. You may want to wear gloves to keep the dye from staining your hands. Knead until smooth. Store it in a plastic bag or container at room temperature.

Source: modernallergymom.blogspot.com