Heat a medium dutch oven over medium heat. Add the butter and 2 tablespoons olive oil and warm until the butter is melted. Add the onions, carrots, celery and a 1/2 teaspoon salt. Cook stirring often for 6 minutes or until the vegetable are soft but have no color. Add the lamb and beef and cook breaking apart the meat with a wooden spoon for 5 minutes or until the meat is cooked through and no longer pink. Stir the garlic, chili paste, red pepper flakes, and tomato paste into the meat mixture. Cook the tomato paste stirring often for 2 minutes. Add the milk. Bring to a simmer and cook for 20 minutes, stirring occasionally until the milk is almost entirely evaporated. Add the wine, tomatoes, bay leaf, parmesan rind and remaining salt. Bring to a simmer and reduce the heat to low to just maintain a gentle simmer. Simmer the sauce for 1 ½ to 2 hours, stirring occasionally to prevent sticking. Skim the oil from the surface.

Spoon the bolognese over creamy polenta reserving any extra to serve on the side. Serve with additional parmesan and a drizzle of olive oil if desire.