Dry short ribs with a paper towel and season with salt and pepper. Set aside.
Turn the Pressure Cooker or Instant Pot on and select sauté (also called "Brown" if using another kind of pressure cooker) and press start. Allow to heat for about a couple minutes and add diced bacon; cook until crisp. Remove bacon bits with a slotted spoon. (Save them for a future salad or omelette!)
Still using the sauté/brown function, add the short ribs to the pot. Sear each side of the ribs until brown. Depending on which model of Instant Pot or Pressure Cooker you have, this will take from 2 - 4 minutes per side. Once browned remove short ribs and set aside. Turn off the pot.
Add red wine, beef stock, garlic cloves and rosemary sprigs to the pot. Give the garlic cloves a good smash with a knife to wake up the flavor. Place short ribs back into the pot.
Place the cover on the pot and select high pressure. Set the time to 10 minutes and press start (see note). Once the time is up and the machine beeps, turn the knob (or button) to release the steam. Allow the steam to fully express before opening the lid.
Remove the short ribs from the cooking liquid and set aside on a plate.
* If making the thickened sauce, tent the short ribs with foil on the plate. If not, allow the short ribs to rest for 5 minutes and serve.
For the thickened sauce
Strain cooking liquid into a medium saucepan and heat over medium-high heat. Bring to a slight boil, stirring frequently. Mix corn starch and water in a shaker bottle and gradually pour into the sauce to help the thickening process.
Drizzle over short ribs.
If you do not use your Instant Pot for cooking the bacon or searing the short ribs, add 3 - 5 minutes to high pressure cooking time since the pot will not be pre-heated.