Legends from Europe
In a large skillet, over medium heat, heat oil and butter; add walnuts. Cook, stirring frequently, until fragrant and beginning to color, about 2 minutes. With a slotted spoon, remove walnuts to a bowl. Increase heat to medium-high. Add Brussels sprouts and onion, cook, stirring constantly, about 8 minutes until golden brown. Stir in prosciutto, add salt and pepper to taste.