In a medium saucepan, mix salt and ⅓ cup water over medium heat, stirring occasionally (about 3-4 minutes). Mixture should appear like slushy, wet snow. Remove from heat.
Add cornstarch and ¼ cup cold water. The mixture will resemble mashed potatoes. Stir till thickens, cool, then knead on a board or countertop that has been lightly dusted wtih cornstarch. If desired, divide dough into smaller balls and add a few drops of food coloring.
Notes
Store unused play dough in the refrigerator in a sealed container with a damp sponge
Recipe by Go Dairy Free at https://www.godairyfree.org/recipes/homemade-fun-with-gluten-free-play-dough