Cook the fries according to the recipe.
While the fries are cooking, melt the butter over medium heat and stir in the flour. Cook for 1 minute to remove the taste of the flour.
Slowly stir in the ale. Adding in stages helps avoid lumps in the final sauce, by not adding too much liquid before the roux has combined with the ale.
Remove from the heat and stir in the cheese, mustard, and Worcestershire sauce. Season with salt to taste.
Preheat an overhead grill.
When the fries are cooked, add them to a deep pie dish, and topped with the hot cheese sauce. Place under the grill and cook until golden brown, and bubbling.
Finish topped with cayenne, chives, and parsley.