Put 2 tablespoons oil in a large, deep saucepan over medium heat. When oil is hot, add minced garlic and cook until fragrant, about 2 minutes. Add onions and continue to cook, stirring frequently, until softened, about 5 more minutes. Add escarole and cook, tossing gently, until it begins to wilt, about another 3 minutes. Add stock and rice to the pan, bring to a boil. Lower the heat, cover and cook about 20 minutes or until rice is tender. Meanwhile, put remaining 2 tablespoons oil in a small skillet. When oil is hot, add sliced garlic and cook over medium-low heat until it turns golden brown and begins to crisp. Remove garlic with a slotted spoon and set aside. When rice is cooked through, season soup with salt and pepper, top with a grating of Parmesan and garnish with garlic slivers.