Bolognese sauce is traditionally made from ground meat, usually a mix of beef and pork, combined with finely chopped onion, celery, and carrot, tomato puree or passata, white or red wine, and milk. Olive oil is used for sautéing the vegetables, and the sauce is seasoned simply with salt and pepper, sometimes fresh herbs like rosemary, then slow-cooked for several hours to develop a rich, thick texture.