Lower the heat to medium - low and continue to cook, whisking frequently, until the mixture has begun to thicken and coats the back of a spoon, leaving a clean, visible trail when you run your finger across the syrup on the spoon (about 5 minutes). (glutenfreeonashoestring.com)
Cook, whisking constantly, over medium - high heat until the whisk leaves a visible trail in the pudding as you whisk it (2 to 3 minutes). (glutenfreeonashoestring.com)
It is ready when the whisk leaves a visible trail as it moves through the roux. (glutenfreeandmore.com)