Preheat the oven to 450°F.
Poke holes in the potatoes with a knife (to prevent them from exploding!). Place them in a large bowl and microwave for 7-10 minutes, tossing every few minutes, until a fork easily pierces through.
In a 15-inch cast iron skillet (or two 9x13-inch baking dishes), combine the potatoes, sausage, and onion. Drizzle with olive oil, season with salt, and toss to coat.
Bake for 15 minutes.
Remove from the oven and add the corn to the skillet. Return to the oven and bake for 10 more minutes.