For the Miso Au Poivre Short Ribs with Mashed Japanese Sweet Potato:

1. Preheat the oven to 325°F.
2. Pat the short ribs dry and season with salt. Heat a large Dutch oven over medium-high heat. Once hot, drizzle in the oil. Working in batches if needed, sear the short ribs in a single layer on all sides until deeply golden brown. Transfer to a plate and set aside.
3. Meanwhile, coarsely grind the black peppercorns using a mortar and pestle or spice grinder.
4. Carefully pour off excess fat from the Dutch oven, leaving about 1 tablespoon behind. Reduce heat to medium and add the shallots and garlic. Sauté for 3–5 minutes, or until softened and fragrant. Add about ¾ of the ground peppercorns and toast for 1 minute, stirring constantly. Pour in the sake and use a wooden spoon to scrape up any browned bits from the bottom of the pan.
5. In a measuring cup, whisk together the chicken broth, miso, soy sauce, and rice vinegar. Return the short ribs to the pot and pour the miso broth mixture over top. Cover, bring to a boil, then transfer to the oven and braise for about 3 hours, or until the short ribs are fork-tender and falling apart.
6. About 1 hour before the short ribs are done, prepare the mashed sweet potatoes. Peel the sweet potatoes and cut them in half lengthwise. Place in a pot, cover with cold water, and season with a pinch of salt. Bring to a boil, then reduce to a simmer and cook for 30–35 minutes, or until tender. Drain and let sit for 2–3 minutes to allow excess moisture to evaporate.
7. Heat the butter and cream together until the butter has melted. Return the sweet potatoes to the pot, add half of the butter-cream mixture, and mash. Gradually add the remaining mixture, mashing until smooth. Season with salt to taste and keep warm.
8. Once the short ribs are done, remove them from the braising liquid and set aside. Pour the liquid into a fat separator or glass measuring cup and place in the freezer for about 10 minutes, until the fat solidifies on top. Skim and discard the fat.
9. Trim excess fat from the short ribs and shred as desired. Return the braising liquid to the pot over medium heat. Once simmering, whisk in the remaining ground peppercorns and the heavy cream.
10. Serve the shredded short ribs over mashed Japanese sweet potatoes, spooning the miso au poivre sauce generously over top. Finish with sliced green onions.