Slice the top off the head of garlic. Put it on a large square of aluminum foil and drizzle 1 teaspoon of the extra-virgin olive oil over the exposed cloves. Wrap the foil around and over the garlic. Roast until it is soft, about 50 minutes to 1 hour. Remove from the oven and let cool.
Pour the 2 cans of broth into a saucepan, over low heat, and add 3 cans of water. Bring to a simmer.
In a large, heavy bottomed skillet, heat the remaining olive oil over medium-high heat. Add the onion and saute for 3 minutes. Add the mushrooms, season with salt and pepper, to taste, and cook until the mushrooms release their juices, about 5 minutes. Add the rice and cook for 1 minute to toast.
Add 2 ladles full of hot broth to the pan and gently stir the rice. Cook until most of the liquid has been absorbed. Adjust the heat so that the pan is just gently bubbling. Continue adding broth and stirring until all the broth is used and the rice is cooked but not mushy, about 20 to 25 minutes. Once the rice has absorbed all the liquid and is nice and creamy, stir in the butter, Parmesan and the garlic pulp. Cover and let rest for 2 minutes. Transfer to a serving dish and serve hot.
Reserve 3 cups for the round 2 recipe, Risotto Cakes.
In a large bowl add the leftover risotto, eggs, corn, bread crumbs, and Parmesan and season with salt and pepper, to taste. Mix to combine well. Form into 12 balls about the size of a walnut, then flatten into patties and arrange on a baking sheet.
Heat the oil in a large nonstick skillet over medium heat. Add the patties and cook until they are golden brown, about 3 to 4 minutes per side. Remove the patties from the oil to a baking sheet lined with a brown bag or paper towels to drain the excess oil. Transfer to a serving tray and serve hot.