Preheat oven to 400 degrees.
Slice ends off of peeled potatoes and then cut them into 1 inch thick round discs. Season them generously with salt and pepper.
Heat a 10 or 12 inch cast iron skillet (or other heavy duty ovenproof skillet) over medium high heat. Add the oil and 4 Tbsp of the butter.
When butter melts and is sizzling (but not brown), lay the potatoes flat on one side and sear them, untouched, until golden brown, about 4 minutes (turn heat down if butter starts to get too dark). Flip the potatoes so browned side is up, then add the broth, rosemary sprigs and garlic cloves. Scatter remaining 4 Tbsp butter, cut into cubes, over the top of the potatoes.
Transfer the skillet to the oven and cook , untouched, until fork tender, about 30 minutes.
Remove from oven (handle will be HOT) and spoon pan juices over the potatoes prior to serving. Discard the rosemary and garlic. Serve hot.
Enjoy!
