Place whole potatoes in a pot and cover with cold water. Add salt and bring to a boil.
Simmer for 30–40 minutes, until fork-tender (soft all the way through).
Drain and let the potatoes steam dry for a few minutes.
Place the potatoes on a baking sheet. Rub with olive oil and salt, then bake at 425°F for 20 minutes.
Transfer the potatoes to plates. Cut them open. Scoop out the inside of 2 potatoes into a bowl, leaving a thin layer inside the skins.
Peel the third potato and add it to the bowl. Add butter, mozzarella, and salt. Mash until smooth and creamy (add 1–2 tablespoons of milk if needed for texture).
Spoon the mashed potatoes back into the potato skins.
Top with sliced hotdogs, olives, and corn. Add chopped green onions. Drizzle with mayonnaise and ketchup, if desired.
Mix while the potatoes are still hot so the butter and cheese melt smoothly into the filling.
Make it yours
Skip ketchup for a more savory version, or swap mayonnaise with yogurt or sour cream for a lighter finish.
Add a mix of fresh, tangy, and creamy toppings: finely sliced red cabbage, pickles or pickled peppers, carrots or corn salad, yogurt-based salads, chili flakes or hot sauce for heat.
Mix and match a few toppings for balance rather than adding too much of one.
At the table
Serve immediately while warm. Add extra toppings on the side for everyone to customize.
Sprinkle a little cheddar on top, if desired. Pair with pickles or a crisp salad to balance the richness.