Add butter to a saucepan and heat over medium heat until melted.
Once butter has melted, add the flour and whisk until mixture begins to bubble and foam. Continue to whisk for another 1 minute.
Slowly pour in the beef stock while whisking constantly.
Once stock is incorporated, whisk in the ketchup, Worcestershire sauce, salt and pepper.
Allow gravy to reach a boil. Meanwhile, combine cornstarch and water to make a slurry.
Once gravy begins to boil, add cornstarch slurry and whisk to combine.
Turn the heat down to medium-low and allow gravy to simmer until the mixture begins to thicken, it should coat the back of a spoon. About 10-15 minutes. Taste the sauce and adjust the seasonings to your liking.
Transfer the fries to your serving plates. Place cheese curds on top of the fries and immediately pour the hot gravy on top so it can melt the curds.
