Place the potatoes in a large pot, cover with cold water and season with salt. Bring to a boil, reduce the heat to medium and simmer until tender, about 20 minutes. Drain well, then cool slightly. Return the potatoes to the pot and, using a masher, mash the potatoes.
Meanwhile, melt the butter in medium, heavy skillet over medium heat. Add the onions and saute until translucent, about 5 minutes. Add the garlic and corn and saute about 5 minutes. Season with salt and pepper. Add the cream and cook over medium-low heat for 3 minutes longer.
Add the sauteed corn to the mashed potatoes and stir to combine until the liquid is fully absorbed. Season with salt and pepper. Serve immediately.