Pre-heat your oven to 450 degrees F and lightly grease a large baking sheet with non-stick spray.
Fill a large pot with cold water and a good helping of salt. Place over high heat and bring to a boil.
As that heats, peel the potatoes and chop into 1/2" thick wedges. Throw in the water. Once the water is boiling, blanch potatoes for 4 minutes. Remove from heat, drain and dry very well. Toss in the duck fat, season well with salt and pepper and arrange as one flat layer on the prepared baking sheet (use 2 if necessary). Place in the oven and bake for 8-10 minutes, flip fries, and continue cooking a further 7-10 minutes or until crispy. Remove from the oven and set aside.
At the same time as you prepare the potatoes, heat 2 Tbsp of butter over medium-low heat in a large frying pan. When it starts to sizzle, add the onions, season with salt, and give the onions a good stir. Cook over this heat, stirring often, until golden and gooey (approx 30 minutes); be careful not to let them burn. Remove from heat and set aside.
Gonna get tricky here - multi-tasking! Once you flip the fries, toss the other 2 Tbsp of butter in a medium sized stock pot. As it starts to sizzle, spoon in the flour and stir stir stir until it becomes fragrant and slightly changes color. Pour in the stock, wine and sprig of rosemary and keep on stirring. The mixture should thicken well and reduce a bit. Season with salt and pepper to taste. Remove what's left of the rosemary stem.
Now build! Throw some hot cooked fries on a plate, layering with the cheese and onions, finishing with a big ladle of gravy.
Eat.....Try not to die of a heart attack.
Recipe by She Eats at https://sheeats.ca/2013/03/ch-ch-ch-changes/