How to Make It
Heat oil in a large skillet over medium-high. Rub pork evenly with 2 teaspoons salt and pepper. Add pork to pan; cook 5 minutes, turning to brown on all sides. Place pork in a 5- to 6-quart slow cooker (do not wipe out pan).
Return pan to medium. Add garlic, rosemary, oregano, and shallots to drippings in pan; cook 3 minutes, stirring occasionally, until shallots are tender and garlic is fragrant. Add tomato paste; cook 1 minute, stirring constantly. Add wine; bring to a boil. Cook 5 minutes or until reduced by half. Combine chicken stock and mustard in a 1-cup glass measure, stirring with a whisk until smooth. Add stock mixture to pan; bring to a boil. Add stock mixture to slow cooker.
Add tomatoes to slow cooker, gently mashing with a spoon. Cover and cook on LOW for 7 hours or until pork is very tender. Place pork on cutting board. Shred into large pieces with two forks.
Increase slow cooker temperature to HIGH. Stir in remaining 1 teaspoon salt, shredded pork, and kale. Cover and cook on HIGH 5 minutes or until kale is tender. Stir in vinegar.
Bring 8 cups water to a boil in a large saucepan over high. Gradually add polenta, stirring with a whisk. Reduce heat and simmer 20 to 30 minutes or until thickened. Serve ragù over polenta.