In a saucepot with a tight-fitting lid, melt butter over medium heat. Add orzo and toast to deep golden in color and fragrant. Stir in rice, add about 2 cups of chicken stock and bring to a simmer. Cover and cook 18 minutes, until rice is just tender, stirring occasionally and adding a bit of water as needed if rice begins to stick.
Bring remaining 6 cups stock plus 2 cups water to a boil in a soup pot. Reduce heat to low, rolling simmer.