Preheat the oven to 350˚F. Poke holes in the potatoes with a fork, then rub them with olive oil and sprinkle with garlic salt, ½ teaspoon kosher salt, and pinch of pepper. Place on a baking sheet and bake until the potatoes are tender and can easily be pierced with a fork, about 55 to 60 minutes.
Cut the potatoes in half lengthwise. One at a time, scoop out the flesh into a bowl, leaving the skins intact. Return the skins back to the baking sheet.
Mash the potatoes with the milk, ricotta, parmesan, butter, garlic, basil, oregano, the remaining 2 teaspoons, salt, and a pinch of pepper. Mix in all but ¼ cup of the pepperoni.
Spoon the potato mixture into the potato skins on the baking sheet. Top each with 1 tablespoon pizza sauce and sprinkle evenly with mozzarella and the rest of the pepperoni. Bake until the cheese is melted, about 10-15 minutes. Serve the potatoes with the remaining sauce.
Notes
You don't have to just use cheese and pepperoni! Mix it up with other toppings like mushrooms, onions, peppers, sausage, or anything you'd like!