In a large bowl, whisk together the flour, salt and cream of tartar.
Add the vegetable oil and boiling water, and using a spatula, mix until combined. Once it’s cool enough to handle, use your hands to knead the playdough in the bowl until it becomes smooth, about 2 minutes. (It may appear wet at first but will dry as you knead and the water gets fully absorbed.)
Turn the playdough onto your work surface and knead it until it is smooth, about 2 minutes.
Use the homemade playdough as is, or if desired, color with food coloring of your choice. (If using food coloring, it’s best to mix the playdough in a bowl while wearing disposable gloves to avoid coloring your hands.)