In a bowl, toss beef chunks with flour until coated.
Add butter to the pressure cooker. Turn on the saute setting at medium heat. When the butter is melted, add beef chunks. Cook until browned on all sides, about 5 minutes, stirring frequently.
Add beef stock to the pot, stirring well and breaking apart any beef bits stuck to the bottom of the pot. Add salt and tomato paste, stirring until dissolved.
Add remaining ingredients (frozen pearl onions, carrots, potatoes, mushrooms) to the pot. Stir.
Close and lock the lid on the pressure cooker. Select the meat/stew function and set the cooking time to 35 minutes. When finished, let sit for 10 minutes to naturally release the pressure before using the steam release handle to vent.
Open the lid and stir. Taste and add additional salt if needed. Serve hot and optionally garnish with chopped parsley.
Recipe from Savory Tooth at https://www.savorytooth.com/instant-pot-beef-stew/