Preheat oven to 300 degrees F. This is to hold the cooked potatoes as you cook in batches.

In a small Dutch oven or cast-iron skillet, heat duck fat to 325 degrees F using a candy or deep-fry thermometer to gauge the heat.

Wash and cut Russets into large thick fries up to ¾ inch wide. Hold in cold water as you cut each potato.

Drain and dry the potatoes thoroughly with paper towels.

Cooking in three batches, place one third of the potatoes in the 325-degree F fat and cook for 6-8 minutes until tender when pierced with a fork. Remove with tongs to a rack that is sitting over a sheet tray. Wait until the fat is up to heat and continue cooking the other two batches.

Bring the heat to about 385 degrees F and add one third of the cooked fries and let the fat settle on 375 degrees F. Try to keep it at that temperature. Once the fries are crisp, about 3-5 minutes, remove to the sheet tray and sprinkle with kosher or sea salt then place the pan in the oven to keep hot. Repeat for the other two batches and serve with the chopped parsley and Parmesan cheese.

If you are making the optional duck gravy to serve along side the fries, heat the stock in a small sauce pan. In a separate small saute pan, melt butter over medium heat, add flour and cook over medium low for two minutes.

Slowly add the butter/flour mixture to the hot stock whisking until the desired thickness is achieved. Season with salt and pepper if needed and serve immediately with the fries.