Cut each potato in half, then in half again, and again in half until you have 8 even chunks. Place in a medium pot with 1 teaspoon salt, cover with cold water and place over high heat.
Bring potatoes to a boil, then lower the heat slightly and boil for ten minutes. Meanwhile, preheat to oven to 425°F.
In a small bowl, mix together polenta, salt and pepper. Drain potatoes well in a colander. Sprinkle with polenta seasoning and toss gently to coat.
In a large (12-inch) cast iron pan or heavy-bottomed skillet, heat olive oil over high heat. When small bubbles begin to rise (but before oil is smoking) and oil is very hot, add rosemary and garlic. Stir carefully with tongs for a minute.
Add seasoned potatoes all at once to the hot, fragrant oil and arrange them with your tongs so that they are evenly distributed around the pan. Place the skillet on the bottom shelf of the hot oven and roast for 10 minutes. Remove pan from oven carefully and turn each potato so the crispy side faces up. Return to oven for another five or ten minutes.
Remove potatoes from oven and, using a slotted spoon, transfer the potatoes to a serving platter and serve at once. Cool, then strain and reserve the oil remaining in the pan for another use.