In a large pot of salted water, bring the potatoes to a boil on a Bull Side Burner. Cover and cook until fork-tender, about 20 minutes. Drain the potatoes, return them to the pot, and cook on medium heat for 2-3 minutes or until the potatoes are dry. Toss the potatoes in the olive oil, butter, and rosemary.
Transfer the potatoes to the preheated griddle & lightly oiled griddle. Using a flat-bottomed heavy glass cup or potato smasher, carefully smash the potatoes until they are about 1/2 inch thick. Turn with a fisher turner or steel spatula and cook for 5-7 minutes, or until the bottoms are golden brown and crispy. Season with salt and pepper to taste.
Remove from the griddle and serve immediately with your favorite garnishes such as sour cream, bacon bits, chives, or herb butter.