In a small bowl, combine salt, paprika and pepper. Rub mixture evenly over ribs. Cut ribs into 4 sections per slab.
In the inner pot of Instant Pot, combine garlic, onion flakes, broth, ketchup, vinegar, Worcestershire sauce and mustard, stirring well.
Add ribs, tossing to coat in sauce, then stand ribs vertically in the pot.
Place the pot inside the cooker housing, close and lock the lid and turn the steam release handle to Sealing. Press Manual and adjust pressure cooking time to 25 minutes.
When the timer beeps, press Cancel and let the pot stand, covered, for 10 minutes. After 10 minutes, turn the steam release handle to Venting and remove the lid. The ribs should be falling off the bone. (If more cooking is needed, reset the manual pressure to “High Pressure” for 5 minutes.)
Transfer ribs to a serving platter and tent with foil to keep warm.
In a small bowl, whisk together cornstarch and cold water.
Press Sauté function on the Instant Pot. Add the cornstarch mixture to the pot and cook, stirring, for 4 minutes or until sauce is thickened.
Season to taste with salt and pepper. Spoon sauce over ribs. Enjoy!