We always keep the skin on if they are in okay condition. If not, you should peel the potatoes. Wash the potatoes thoroughly and cut them into small pieces about 1x1.5 cm. Boil them for 3 minutes in water with a little added vinegar (if you don't have vinegar, you can use salt). Take the potatoes out and let them dry in a colander for 5 minutes.  Optionally, dry them off afterwards with a dish towel. Find a thick-bottomed (large) pan and heat the fat over medium heat. Add the potatoes, along with thyme and rosemary. Let it cook for 20 minutes, turning them regularly. For the last 5 minutes, turn the heat up to almost maximum and again turn often. When they have reached the desired color, put them back in a colander and dab them dry with a dish towel/paper towel. Season them with salt and pepper, and they are ready to serve.