Add the chili flakes, tomato sauce, half of the onion, garlic, and 1/2 tsp of salt to a blender. Blend until smooth, stir into beef broth.
Heat olive oil in a Dutch oven over medium-high heat. Sprinkle short ribs generously with salt and pepper. Sear the short ribs until browned on each side, 2-3 minutes per side. If needed, do this in batches so that they are not crowded. Set ribs aside.
Sauté the remaining half of onion slices until softened a bit.
Add the bottle of cider to the pan, bring it to a boil and scrape up any browned bits on the bottom of the pot.
Add the blended sauce mixture, bring to a boil, cook 2-3 minutes.
Return the short ribs to the pot (along with any juices that may have come out). Add the rosemary, cover. Bake at 325 for 2 ½ hours, or until the meat comes off the bone.
Remove the ribs and cover with foil. Place Dutch oven back onto the stove, and reduce the sauce until its nice and thick (about 15 min). Meanwhile, make the cheesy grits.
Cheesy Grits
Place water, milk, and salt into a medium saucepan. Bring to a gentle simmer.
Whisk in grits, continuously stir until thickened (about 5 min).