We used a very basic recipe I found online. Just 1 cup of cornstarch, 3 cups water, and food coloring. You boil the water, dissolve the cornstarch in some water separately, remove boiling water from the heat, add dissolved cornstarch and then stir for a minute until it becomes clear.
I am not sure if it was a user error or if the recipe wasn't the greatest. I might not have stirred it long enough, but it was really thick. Perhaps it was too much cornstarch. It was really goopy and slightly lumpy. My toddler still had fun with it even though it didn't quite do the job. I also don't have a lot of finger painting experience so I am not quite sure how it is supposed to be. You can see the flower I painted represents how goopy and lumpy it was.
Here is my dear son giving a demonstration: