Special equipment: rice cooker
In a rice cooker, mix the rice, stock, water, and 1 tablespoon butter. Cover and cook according to machine instructions. Meanwhile, in a small saute pan over low heat, saute the onion in the remaining 3 tablespoons butter until soft and sweet, stirring occasionally, about 15 minutes. Set aside. When the rice is done, toss the rice with the onion butter and serve.