Cook sprouts in boiling, salted water for about 5 minutes. Drain. In large saucepan or fry pan, melt 6 tablespoons of butter over medium-high heat. Add shallots and garlic and cook for 1 minute. Add sprouts in one layer and cook until golden brown, about 5 minutes. Remove from pan. Add remaining butter and, when melted, add walnuts. Cook, stirring, until golden and fragrant, about 2 minutes. Add lemon juice, salt, pepper and sprouts and stir well to coat and warm through. Transfer to serving bowl and sprinkle with parmesan.