Heat the oil in the pressure cooker over medium-high heat until hot. Add the chicken pieces and cook until golden-brown on all sides. Transfer chicken to a plate.
Mix the 1 cup water and 2 bouillion cubes, until dissolved.
Add the onion, paprika, and bouillion and stir to mix. Add the chicken pieces back to the pot and add the tomato on top, but don't stir it inches Add the salt.
Lock on the lid and bring to pressure over high heat. Reduce heat to medium and cook for about 7 minutes. Remove from heat and let sit for 5 minutes to finish cooking.
Gently release any remaining pressure and transfer the chicken to a plate.
Whisk the sour cream in a small bowl until smooth. Add 1/4 cup of the liquid from the pot and whisk until smooth.
Put the pot back on a burner over medium heat, until sauce is lightly bubbling. Pour the sour cream mixture into the pot and whisk to mix.
Whisk together the 1/2 cup of water and cornstarch. Slowly add this to the pot and whisk it in until the sauce is not quite as thick as gravy. You may not use all the water/cornstarch mixture. Add the chicken pieces back to the pot.