Season the beef generously with salt and pepper. Select Browning/Saute to preheat the pressure cooking pot. When hot, add 1 tablespoon oil. Brown the meat in batches, about 3 minutes per batch, until all of the meat is browned. Add more oil as needed. Do not crowd the pot. Transfer the browned meat to a plate.
Add the remaining 1 tablespoon oil and butter to the cooking pot. When the butter melts, add the mushrooms. Cook for about 5 minutes until golden, stirring only to prevent burning and thus allowing the most browning. Transfer to a separate bowl and set aside.
Add the onion to the cooking pot. Saute for about 3 minutes, stirring frequently, until soft and beginning to brown. Add the garlic and tomato paste. Saute for 1 minute. Stir in the beef broth to deglaze the pot, scraping up any brown bits from the bottom. Add the browned beef and accumulated juices. Lock the lid in place. Select High Pressure and 18 minutes cook time.
When the cook time ends, turn off the pressure cooker. Let the pressure release naturally for 10 minutes and finish with a quick pressure release. When the valve drops, carefully remove the lid.
In a small bowl, whisk the cornstarch and cold water until smooth. Add the slurry to the pot. Select Simmer/Saute and bring the gravy to a boil, stirring constantly until it thickens. Add the sour cream and the cooked mushrooms to the cooking pot and stir until blended. Serve over egg noodles.