Preheat your oven to 450°F and place a large, heavy skillet or roasting pan in the oven to warm up. In a large pot, cover the potatoes with cold, salted water and bring to a boil over high heat. Once boiling, reduce the heat and let them simmer for 5 minutes.

Drain the potatoes thoroughly and let them dry on paper towels. Spread the flour on a plate and, once the potatoes are dry, roll them in the flour to coat, shaking off any excess. Carefully remove the hot skillet from the oven, add the oil and then the potatoes. Roast in the oven, occasionally shaking the pan, until the potatoes are evenly golden brown, about 30 minutes.

After roasting, remove the pan from the oven and mix in the garlic, sage, and butter. Return the pan to the oven for an additional minute. Season with salt and pepper to taste and serve.