Scrub your potatoes and pierce each a few times with a fork. Line a sheet pan with parchment and place the potatoes on the sheet pan. Bake for 1 hour or until a knife easily passes through without resistance, turning halfway through the baking time.
Step 3
Remove potatoes from oven, and turn your oven to broil.
Step 4
Using a sharp knife, carefully slice the potatoes in half and scoop the flesh into a large pot. Add the butter and duck fat, and mash with a potato masher to combine. Add the sour cream, hot milk, and cream, and whip just until smooth (do not overmix; the mixture may become gluey). With a wooden spoon, stir in half the cheddar cheese and green onions, along with the salt and pepper. Taste and correct seasoning.
Step 5
Line a sheet pan with foil. Fill each potato half with mashed potato mix, and place on the foil-lined sheet pan. Top with remaining cheese and green onions, and broil for 2-3 minutes, watching carefully, until the cheese is melted and has browned in spots. Serve immediately.