Prepare fries and veggies burgers as directions instruct. I'll often make a batch of the veggies burgers (these ones) ahead of time and freeze them for use whenever I like.
In a medium sauce pan, combine cheddar cheese and cornstarch in a small pot. Heat over medium low and stir until cheddar begins to melt. Add 6 tablespoons milk (or beer), Worcestershire, mustard and garlic powder, stir until mixture comes together. Add more milk (or beer), 1-2 tablespoon at a time, stirring frequently, to reach a pourable cheese sauce, 4 to 5 minutes.
Assemble the ponyshoe by topping the burger with a heap of fries drizzle of cheese sauce, grilled onions (if desired), and serve with a side of ketchup.