Wash and dry the chicken fillet, then cut into 1 cm thick pieces.
Lightly pound each piece to tenderize, then cut into strips.
In a saucepan, combine sour cream, tomato paste, and broth. Season with salt and pepper to taste. Bring to a boil, then turn off the heat and set aside.
Coat the chicken pieces in flour, then place in a colander and shake off excess flour.
Heat 2 tbsp vegetable oil in a large pan over medium heat. Chop the onions and add them to the pan. Cook for 2-3 minutes until softened.
Add the floured chicken to the onions and cook over medium-high heat, stirring constantly for 5-6 minutes.
Transfer the chicken and onions to the saucepan with the sauce. Place over low heat and simmer for 20 minutes until the chicken is cooked through (internal temperature 74°C/165°F).