Season short ribs on all sides with salt and pepper. Select sear/sauté on pressure cooker and set to high & select start. Heat 2 tbsp of oil in the pot until hot, approx. 3-4 minutes.
Add short ribs to pot and brown each side for 4 minutes until browned on all sides. Remove when done.
Heat 1 tbsp olive oil in the pot. Add the onions and sauté until softened, 2-3 minutes. Add garlic and cook another minute until soft and fragrant.
Add chopped carrots, celery, thyme, salt, and pepper to the pot and sauté for 2-3 minutes. Add wine and cook for another 1-2 minutes.
Add short ribs back into the pot, keeping them in one layer if possible. Add broth, sugar, and bay leaves.
Set pressure to high and set timer for 45 minutes
When pressure cooking is complete, natural release the pressure for 15 minutes. After 15 minutes, quick release to vent and remove lid after unit has finished releasing pressure.
Carefully remove ribs and vegetables with a slotted spoon and transfer to a serving tray. Set sear/sauté to high and bring the sauce to simmer. Mix 1 tbsp cornstarch and 1 tbsp of water together in a small bowl or ramekin and add to the sauce to thicken to the desired consistency.
Serve short ribs over polenta or mashed potatoes with vegetables and sauce.