Wash and pat dry the potatoes. Using a fork, pierce the potatoes, then microwave them for 10 to 15 minutes, or until they are tender.
Remove the casings from the sausages. In a large skillet, heat 1 tablespoon of olive oil over high heat. Sauté the sausage meat for 5 minutes, breaking it apart with a spoon and stirring frequently. Set aside.
Once the potatoes are cooked, scoop out the flesh and place it in a large bowl. Add the milk and mash everything together using a potato masher.
Next, mix the cooked sausage, chopped spinach, grated cheddar cheese, salt, and pepper into the bowl with the mashed potatoes. Stir all the ingredients well until you have a uniform mixture.
Fill the potato skins with the prepared mixture. Sprinkle a generous amount of grated cheese on top.
Place the stuffed potatoes in a preheated oven at 400°F (200°C) for about 15 minutes, or until they are nicely golden.