Melt butter in a large skillet. Add onion and season generously to taste with salt and pepper. Cook over medium-low heat for about 8 minutes, until translucent. Add the sliced green onion and cook an additional 2 minutes.
Slowly add the rice and continue cooking for 3 minutes, stirring frequently. Pour in the chicken stock, increase heat to high and bring to a boil. Cover and reduce heat to low. Simmer for 15 minutes, until stock is absorbed and rice is te