Season short ribs with a generous sprinkling of salt and pepper. Let sit for 30 minutes.
Turn on the saute setting on the instant pot. When warm, add oil. Add the short ribs and sear until browned on all sides, about 10 minutes. Remove the short ribs and set them aside.
Add onion and saute until translucent and softened, about 4-5 minutes. Add back the short ribs, along with garlic, white wine, apple cider, beef broth, bay leaf, rosemary, white balsamic vinegar, and brown sugar. Close the instant pot and set it to pressure cook on high for 1 hour.
Meanwhile, make the lemon herb sauce. Combine chopped parsley with the juice of ½ lemon, lemon zest, red chili flakes, and olive oil. Season with salt and pepper and let sit for at least 30 minutes.
Make the mashed potatoes. Place potatoes in a large pot and fill with enough water to cover. Season the water with salt and bring it to a boil over high heat. Cover the pot, reduce the heat to medium, and continue to simmer until the potatoes are fork-tender.
Heat milk with butter and minced garlic in a medium pot over low heat.
Drain the potatoes and mash them. Add the milk and butter mixture, mashing until the potatoes are smooth. Stir in creme fraiche and season the potatoes with salt. Keep warm.
Let the short ribs natural release steam for 10 minutes, then release the pressure. Remove short ribs and skim the fat from the braising liquid. Turn on the saute setting on the instant pot and let it simmer until the liquid has reduced by half. Turn off and add butter, whisking until incorporated. Season sauce with salt and pepper.
Spoon the mashed potatoes onto two plates and place the short ribs on top, spooning the sauce on top. Drizzle on the lemon herb sauce and serve immediately.
Notes
You can prepare the lemon herb sauce the day before.This recipe can be prepared on the stovetop. Follow the directions until step 3, adding all of the ingredients in a Dutch oven. Bring the liquid to a boil, then transfer to a preheated oven at 325 degrees F. Continue to cook for 2 ½ hours or until the beef falls apart easily from the bone.