Step 1

For the gravy: Melt the butter in a small saucepan over medium heat. Add the flour and whisk to combine. Cook the flour until dark brown, 5 to 7 minutes. Add the stock and cook, whisking, until the mixture is smooth and thickened enough to coat the back of a spoon, 7 to 10 minutes. Stir in the sherry, Worcestershire, 1/2 teaspoon salt and some pepper, adjusting the seasoning to taste. Remove from the heat and cover by pressing a piece of plastic wrap directly onto the surface of the gravy, taking care to cover it completely to prevent a skin from forming. Set aside.

Step 2

For the fries: Bake the French fries according to the manufacturer's instructions.

Step 3

For the cheese sauce: Melt the butter in a small saucepan over medium heat. Add the flour and whisk to combine. Cook until the mixture resembles sand, about 3 minutes. Add the milk and cook, whisking constantly, until the mixture begins to boil and thicken, 2 to 4 minutes. Add the Cheddar and Gruyere and continue to cook, stirring, until the cheese is fully melted, another 2 to 3 minutes. Add the Worcestershire, 1/4 teaspoon salt and pepper to taste and remove from the heat. Cover in the same fashion as the gravy and set aside until the French fries are ready.

Step 4

When the French fries are ready, transfer them to a serving platter. Drizzle the fries with the warm gravy and then with the warm cheese sauce. Serve immediately.