Heat oil in a medium Dutch oven over medium heat until simmering. Add pancetta and cook, stirring often, until fat has rendered, 10 to 12 minutes. Add carrot, onion, and celery and season with salt and pepper. Cook, stirring occasionally, until vegetables are soft and lightly browned, about 10 minutes.

Add ground beef and merguez sausage and increase heat to medium-high. Cook, stirring to break meat into small pieces, until browned, 12 to 15 minutes. Drain excess fat as needed.

Add Chianti and cook until liquid has almost evaporated. Reduce heat to medium and stir in tomato paste. Cook until sauce turns dark red, 3 to 5 minutes. Add enough milk to barely cover the meat. Continue to cook, stirring occasionally, until milk has evaporated and the mixture turns into a thick rich sauce, 1 to 1 1/2 hours. Adjust salt and pepper, if necessary.