Recipe(tried): Burgerville Spread - To thicken...

I use arrowroot powder to thicken sauces like this. Dissolve 1 tsp of arrowroot powder in 1 tbsp water, then bring to a boil in the microwave. Stir in a little of the the sauce, mixing well, then add the remaining sauce and stir until well mixed. Let stand for a couple of minutes.

Arrowroot powder is available in the spices and herbs section of grocery stores, but is cheaper by the ounce in the small bulk jars that most grocery stores have to one side of the bulk bins.

Apart from the arrowroot powder, my version of this recipe is much the same, except that I add 1 tsp of ketchup for color and sweetness, and I use Vegenaise.