Grind pecans with broth in blender. Melt butter in large saucepan; add onions and cook five minutes over medium heat until soft. Add garlic and cook one minute. Slowly add nut/broth mixture, tomato puree and cornstarch. Cook 30 minutes, uncovered, on low heat. Beat egg yolk into cream and slowly whisk into soup; do not boil after this point. Season with salt, pepper and nutmeg.