Cut potatoes to resemble scallops. Place in cold water for 5 minutes to remove starch. Dry potatoes.
Heat cast iron skillet on high heat with vegetable oil. When oil is shiny add potatoes. Season with salt and pepper. Roast for 5 minutes.
Flip potatoes over and use paper towels to soak up excess oil. Add butter and thyme. Season other side with salt and pepper.
Roast until butter becomes golden. Transfer to oven for 30 min or until potatoes are soft and creamy on the inside. If potatoes are dry add a splash of more broth.