Slice potatoes into strips and place in a large bowl. Cover with water and place in the fridge for at least 2 hours, up to 12 hours.
Pour enough oil into a large sturdy pot to reach about two-thirds the way up the side. Heat the oil to 320°F.
Drain the potatoes and thoroughly dry with paper towels or a kitchen towel.
Working in batches, place a handful of the potatoes in the hot oil and cook, stirring frequently, until just starting to brown and beginning to get a little crisp, about 5 to 6 minutes. Remove with metal tongs or a spider and drain on paper towels. Repeat with remaining potatoes. Let the potatoes rest for about 20 minutes while you make the gravy.
Melt the butter over medium heat in a large skillet. Add the shallots and cook until tender, about 4 minutes. Add the garlic and sauté for another 30 seconds, stirring, frequently.
Stir in the flour and let cook for about 1 minute, stirring often.
Carefully whisk in the beef stock, ketchup, vinegar, Worcestershire sauce, salt, and pepper. Bring to a boil, and then reduce the heat. Continue stirring until thickened, about 3 to 5 minutes. Set aside, but keep warm.
Increase the heat on the oil until it reaches 375°F.
Working in batches, place the partially cooked fries in the hot oil. Fry until golden and crisp, about 2 to 3 minutes. Transfer to paper towels and sprinkle all over with salt.
Place all of the fries on a platter. Nestle about half of the curds throughout the fries. Ladle the hot gravy all over the fries and curds. Add the rest of the curds and top with more gravy and the sliced scallions. Serve immediately. (You may have some gravy leftover for another use).