In a large non-stick skillet over high heat, brown the onions in the oil. Add the thyme. Season with salt and pepper. Set aside.
Line the bottom of the slow cooker with a third of the potato slices. Season with salt and pepper. Cover with half of the onions. Continue with a third of the potatoes and the remaining onions. Drizzle with the broth and finish with the remaining potatoes. Press lightly. Season with salt and pepper. Brush with the melted butter.
Cover and cook on Low for 6 hours. It can be maintained on Warm for up to 4 hours.
