How to Make It
Cut pork in half crosswise. Combine pepper and next 4 ingredients (through thyme). Rub seasoning mixture over surface of pork halves.
Heat a large Dutch oven over medium-high heat. Add oil to pan; swirl to coat. Add pork to pan; cook 5 minutes, browning on all sides. Transfer pork to the inner pot of a 6-quart Instant Pot®. Add onion, leek, and carrot to pan; cook, stirring constantly, 5 minutes or until vegetables are golden. Stir in wine, broth, and 1/3 cup water, scraping pan to loosen browned bits. Pour onion mixture over pork in cooker; add plums and bay leaves.
Close and lock the lid of the Instant Pot®. Turn the steam release handle to "Venting" position. Press [Slow Cook], and use [Adjust] to select "More" mode. Press [-] or [+] to choose 1 hour cook time. When time is up, turn cooker off. Press [Slow Cook], and use [Adjust] to select "Less" mode. Press [-] or [+] to choose 5 hours cook time. (Cook additional time, if necessary, until pork is tender.)
Remove pork from cooker; keep warm. Combine cornstarch and 2 tablespoons water in a small bowl; stir well. Add cornstarch mixture to cooking liquid in cooker. Turn cooker off.
Press [Sauté], and use [Adjust] to select "More" mode. Bring mixture to a boil, and cook 15 minutes or until sauce is thick, stirring frequently. Discard bay leaves. Slice pork, and serve with sauce. Garnish with thyme leaves, if desired.