bring broth, 2 tablespoons butter, saffron, and 1/4 teaspoon coarse salt to boil in heavy large saucepan, stirring to melt butter.
Remove from heat. Mix in couscous. Cover and let stand until all liquid is absorbed and couscous is tender, about 10 minutes. Fluff couscous with fork. Mix in remaining 1 tablespoon butter and half of green onions and nuts. Seanson to taste with salt and pepper. Mound in bowl. Sprinkle with remaining green onions and nuts.