Use a large sauté pan to heat the oil over medium heat. Add the onions and season with salt and pepper. Cook, stirring, until the onions soften, about three minutes.
Add the stock and the garlic. Bring the mixture to a boil, reduce the heat to medium, and continue to simmer for another 5-7 minutes.
Add the rice and simmer for about another 10 minutes, stirring constantly. The mixture should become creamy and bubbly in about 8 minutes.
Stir in the cream, the butter, the green onions, cheese. Simmer for about another 2 minutes, stirring the whole time.
Remove the skillet from the heat and spoon the risotto into the center of about eight bowls.
Garnish with freshly shaved black truffle.