In a medium saucepan, bring the vegetable stock and 2 cups of water just to a boil; keep warm. In a large saucepan, melt 4 tablespoons of the butter. Add the onion, garlic and a generous pinch of salt and cook over moderate heat, stirring occasionally, until softened, about 5 minutes. Add the rice and cook, stirring, until coated and opaque, about 3 minutes. Add the wine and cook, stirring, until absorbed, about 7 minutes. Add half of the warm vegetable stock and cook over moderately low heat, stirring, until nearly absorbed, about 7 minutes. Add the remaining vegetable stock and cook, stirring, until nearly absorbed and the rice is al dente, 8 to 10 minutes longer.