Season all sides of the Beef Short Ribs (2.5 pound) with Kosher Salt (2 teaspoon), Ground Black Pepper (1 1/2 teaspoon) and Garlic Powder (1 tablespoon).
Set your pressure cooker to sauté and 375 degrees F (190 degrees C) if your unit can adjust the temperature. Add Olive Oil (2 1/2 tablespoon) and sear all sides of the short ribs until golden brown. Remove ribs and set aside.
Add Balsamic Vinegar (1/4 cup) and Beef Stock (1 cup) to the pot and deglaze by whisking up the brown bits from the bottom.
Add ribs, chopped Onion (1), chopped Carrot (2), Portabella Mushroom Cap (1), and Tomato Paste (6 ounce). Stir until tomato paste has dissolved.
Return the short ribs to the pressure cooker and pressure cook on the meat function for 30 to 40 minutes.
Allow short ribs to sit for 15 minutes before doing a pressure release. This prevents the final outcome of the short ribs from becoming tough.
Combin the Corn Starch (3 tablespoon) and Water (3 tablespoon) and whisk until there are no lumps.
Remove the ribs and skim any fat from the top of the liquid in the pot. Set the pressure cooker to saute, bring the liquid to a boil, then stir in cornstarch and water mixture. Taste for Salt and Pepper (to taste) and return the short ribs. Cook on low sauté heat for 5 minutes.
Garnish with Fresh Parsley (to taste). Serve with egg noodles, rice or mashed potatoes.